diff --git a/exercises/B-hello-world/README.md b/exercises/B-hello-world/README.md
index 27282c4af..85cd05bc6 100644
--- a/exercises/B-hello-world/README.md
+++ b/exercises/B-hello-world/README.md
@@ -14,5 +14,5 @@ Inside of `exercise.js` there's a line of code that will print "Hello world!".
 
 - Try to `console.log()` something different. For example, 'Hello World. I just started learning JavaScript!'.
 - Try to console.log() several things at once.
-- What happens when you get rid of the quote marks?
-- What happens when you console.log() just a number without quotes?
+- What happens when you get rid of the quote marks? Face with SyntaxError(missing ) after argument list)
+- What happens when you console.log() just a number without quotes? Face with SyntaxError(missing ) after argument list)
diff --git a/exercises/B-hello-world/exercise.js b/exercises/B-hello-world/exercise.js
index b179ee953..ae6f53018 100644
--- a/exercises/B-hello-world/exercise.js
+++ b/exercises/B-hello-world/exercise.js
@@ -1 +1 @@
-console.log("Hello world");
+console.log("Hello World. I just started learning JavaScript!" );
diff --git a/exercises/C-variables/exercise.js b/exercises/C-variables/exercise.js
index a6bbb9786..1bab81a4f 100644
--- a/exercises/C-variables/exercise.js
+++ b/exercises/C-variables/exercise.js
@@ -1,3 +1,5 @@
 // Start by creating a variable `greeting`
-
+let greeting="Hi Leila"
 console.log(greeting);
+console.log(greeting);
+console.log(greeting);
\ No newline at end of file
diff --git a/exercises/D-strings/exercise.js b/exercises/D-strings/exercise.js
index 2cffa6a81..07334b5cd 100644
--- a/exercises/D-strings/exercise.js
+++ b/exercises/D-strings/exercise.js
@@ -1,3 +1,6 @@
 // Start by creating a variable `message`
-
+let message="this is a string"
+let messageType=typeof message;
 console.log(message);
+console.log(messageType);
+// console.log(message + " "+ typeof message);
diff --git a/exercises/E-strings-concatenation/exercise.js b/exercises/E-strings-concatenation/exercise.js
index 2cffa6a81..6c583f835 100644
--- a/exercises/E-strings-concatenation/exercise.js
+++ b/exercises/E-strings-concatenation/exercise.js
@@ -1,3 +1,5 @@
 // Start by creating a variable `message`
-
-console.log(message);
+let greetingSentence ="Hi my name is";
+let name="Leila";
+let greeting =greetingSentence +" " + name;
+console.log(greeting);
diff --git a/exercises/F-strings-methods/exercise.js b/exercises/F-strings-methods/exercise.js
index 2cffa6a81..0f2978cee 100644
--- a/exercises/F-strings-methods/exercise.js
+++ b/exercises/F-strings-methods/exercise.js
@@ -1,3 +1,4 @@
 // Start by creating a variable `message`
-
-console.log(message);
+let name="Leila";
+let message=name.length;
+console.log("My name is"+" "+name + " "+ "and my name is"+" " + message+" "+ "character long.");
diff --git a/exercises/F-strings-methods/exercise2.js b/exercises/F-strings-methods/exercise2.js
index b4b46943d..2541d2045 100644
--- a/exercises/F-strings-methods/exercise2.js
+++ b/exercises/F-strings-methods/exercise2.js
@@ -1,3 +1,3 @@
 const name = " Daniel  ";
-
-console.log(message);
+const message=name.length;
+console.log("My name is" + " " + name.trim() + " " + "and my name is" + " " + message + " " +"character long.");
diff --git a/exercises/G-numbers/exercise.js b/exercises/G-numbers/exercise.js
index 49e7bc00b..34bfd982f 100644
--- a/exercises/G-numbers/exercise.js
+++ b/exercises/G-numbers/exercise.js
@@ -1 +1,5 @@
 // Start by creating a variables `numberOfStudents` and `numberOfMentors`
+const numberOfStudents=10;
+const numberOfMentors=7;
+const sum=numberOfStudents+numberOfMentors;
+console.log("Total number of students and mentors:" + sum);
\ No newline at end of file
diff --git a/exercises/I-floats/exercise.js b/exercises/I-floats/exercise.js
index a5bbcd852..ebbd200c1 100644
--- a/exercises/I-floats/exercise.js
+++ b/exercises/I-floats/exercise.js
@@ -1,2 +1,8 @@
 var numberOfStudents = 15;
 var numberOfMentors = 8;
+var total = numberOfMentors + numberOfStudents;
+let studentPerc = Math.round((numberOfMentors / total) * 100);
+let mentorPerc = Math.round((numberOfStudents / total) * 100);
+
+console.log("Percent of student :" + " " + studentPerc + "%");
+console.log("Percent of mentor :" + " " + mentorPerc + "%");
diff --git a/exercises/J-functions/exercise.js b/exercises/J-functions/exercise.js
index 0ae5850e5..e9ba2f0ef 100644
--- a/exercises/J-functions/exercise.js
+++ b/exercises/J-functions/exercise.js
@@ -1,5 +1,6 @@
 function halve(number) {
   // complete the function here
+  return number/2;
 }
 
 var result = halve(12);
diff --git a/exercises/J-functions/exercise2.js b/exercises/J-functions/exercise2.js
index 82ef5e780..6d216ffc6 100644
--- a/exercises/J-functions/exercise2.js
+++ b/exercises/J-functions/exercise2.js
@@ -1,5 +1,6 @@
 function triple(number) {
   // complete function here
+  return number*3;
 }
 
 var result = triple(12);
diff --git a/exercises/K-functions-parameters/exercise.js b/exercises/K-functions-parameters/exercise.js
index 8d5db5e69..e37f89d44 100644
--- a/exercises/K-functions-parameters/exercise.js
+++ b/exercises/K-functions-parameters/exercise.js
@@ -1,6 +1,7 @@
 // Complete the function so that it takes input parameters
-function multiply() {
+function multiply(a,b) {
   // Calculate the result of the function and return it
+  return a*b;
 }
 
 // Assign the result of calling the function the variable `result`
diff --git a/exercises/K-functions-parameters/exercise2.js b/exercises/K-functions-parameters/exercise2.js
index db7a8904b..e7c787d04 100644
--- a/exercises/K-functions-parameters/exercise2.js
+++ b/exercises/K-functions-parameters/exercise2.js
@@ -1,5 +1,7 @@
 // Declare your function first
-
+function divide(a, b) {
+  return a / b;
+}
 var result = divide(3, 4);
 
 console.log(result);
diff --git a/exercises/K-functions-parameters/exercise3.js b/exercises/K-functions-parameters/exercise3.js
index 537e9f4ec..d1728ae72 100644
--- a/exercises/K-functions-parameters/exercise3.js
+++ b/exercises/K-functions-parameters/exercise3.js
@@ -1,5 +1,7 @@
 // Write your function here
-
+function createGreeting(name){
+    return "Hello, My name is " + name;
+}
 var greeting = createGreeting("Daniel");
 
 console.log(greeting);
diff --git a/exercises/K-functions-parameters/exercise4.js b/exercises/K-functions-parameters/exercise4.js
index 7ab44589e..56b4cc834 100644
--- a/exercises/K-functions-parameters/exercise4.js
+++ b/exercises/K-functions-parameters/exercise4.js
@@ -1,5 +1,7 @@
 // Declare your function first
-
+function add(a,b){
+    return a+b;
+}
 // Call the function and assign to a variable `sum`
-
+sum=add(13,124);
 console.log(sum);
diff --git a/exercises/K-functions-parameters/exercise5.js b/exercises/K-functions-parameters/exercise5.js
index 7c5bcd605..f399b6bf6 100644
--- a/exercises/K-functions-parameters/exercise5.js
+++ b/exercises/K-functions-parameters/exercise5.js
@@ -1,5 +1,7 @@
 // Declare your function here
-
+function createLongGreeting(name,age){
+    return "Hello, my name is " + name + " and I'm " + age + " years old";
+}
 const greeting = createLongGreeting("Daniel", 30);
 
 console.log(greeting);
diff --git a/exercises/L-functions-nested/exercise.js b/exercises/L-functions-nested/exercise.js
index a5d377442..60bab6ebd 100644
--- a/exercises/L-functions-nested/exercise.js
+++ b/exercises/L-functions-nested/exercise.js
@@ -1,5 +1,26 @@
+
+var greet="HELLO";
 var mentor1 = "Daniel";
 var mentor2 = "Irina";
 var mentor3 = "Mimi";
 var mentor4 = "Rob";
 var mentor5 = "Yohannes";
+
+
+function upperCase(name){
+    
+    return name.toUpperCase();
+}
+function showName(greet,name){
+    return greet +" "+ upperCase(name);
+}
+let result1=showName(greet,mentor1);
+let result2 = showName(greet, mentor2);
+let result3 = showName(greet, mentor3);
+let result4 = showName(greet, mentor4);
+let result5 = showName(greet, mentor5);
+console.log(result1);
+console.log(result2);
+console.log(result3);
+console.log(result4);
+console.log(result5);
\ No newline at end of file
diff --git a/extra/1-currency-conversion.js b/extra/1-currency-conversion.js
index 75b3c6aab..b80492a6a 100644
--- a/extra/1-currency-conversion.js
+++ b/extra/1-currency-conversion.js
@@ -5,7 +5,10 @@
   Write a function that converts a price to USD (exchange rate is 1.4 $ to £)
 */
 
-function convertToUSD() {}
+function convertToUSD(price) {
+  price *=1.4;
+  return price;
+}
 
 /*
   CURRENCY CONVERSION
@@ -15,7 +18,11 @@ function convertToUSD() {}
   They have also decided that they should add a 1% fee to all foreign transactions, which means you only convert 99% of the £ to BRL.
 */
 
-function convertToBRL() {}
+function convertToBRL(price) {
+  price*=5.7;
+  total=(price-(price*1/100)).toFixed(2);
+  return +total;
+}
 
 /* ======= TESTS - DO NOT MODIFY ===== 
 There are some Tests in this file that will help you work out if your code is working.
diff --git a/extra/2-piping.js b/extra/2-piping.js
index b4f8c4c1b..61ea616cf 100644
--- a/extra/2-piping.js
+++ b/extra/2-piping.js
@@ -16,26 +16,29 @@
   the final result to the variable goodCode
 */
 
-function add() {
-
+function add(num1,num2) {
+  return num1+num2;
 }
 
-function multiply() {
-
+function multiply(num1,num2) {
+  return num1*num2;
 }
 
-function format() {
-
+function format(number) {
+  return `£${number.toString()}`
 }
 
 const startingValue = 2;
 
 // Why can this code be seen as bad practice? Comment your answer.
-let badCode =
+let badCode = `£${(startingValue+10)*2}`
+
 
-/* BETTER PRACTICE */
 
-let goodCode =
+/* BETTER PRACTICE */
+const sum=startingValue+10;
+const result=sum*2;
+let goodCode =`£${result}`;
 
 /* ======= TESTS - DO NOT MODIFY ===== 
 There are some Tests in this file that will help you work out if your code is working.
diff --git a/extra/3-magic-8-ball.js b/extra/3-magic-8-ball.js
index 46f65f928..f597682ee 100644
--- a/extra/3-magic-8-ball.js
+++ b/extra/3-magic-8-ball.js
@@ -45,10 +45,40 @@
 
 // This should log "The ball has shaken!"
 // and return the answer.
+let fixAnswer = [
+  "It is certain.", //0
+  "It is decidedly so.", //1
+  "Without a doubt.", //2
+  "Yes - definitely.", //3
+  "You may rely on it.", //4-very positive
+  "As I see it, yes.", //5
+  "Most likely.", //6
+  "Outlook good.", //7
+  "Yes.", //8
+  "Signs point to yes.", //9-positive
+  "Reply hazy, try again.", //10
+  "Ask again later.", //11
+  "Better not tell you now.", //12
+  "Cannot predict now.", //13
+  "Concentrate and ask again.", //14-negetive
+  " Don't count on it.", //15
+  "My reply is no.", //16
+  "My sources say no.", //17
+  "Outlook not so good.", //18
+  " Very doubtful.", //19-very negetive
+];
+
+
 function shakeBall() {
   //Write your code in here
+  console.log("The ball has shaken!");
+  randomNumber = Math.floor(Math.random() * fixAnswer.length);
+  result =fixAnswer[randomNumber];
+   return result;
 }
 
+
+
 /* 
   This function should say whether the answer it is given is
     - very positive
@@ -58,10 +88,25 @@ function shakeBall() {
 
   This function should expect to be called with any value which was returned by the shakeBall function.
 */
-function checkAnswer(answer) {
-  //Write your code in here
-}
 
+ function checkAnswer(answer) {
+   //Write your code in here
+   let ballPredict = fixAnswer.indexOf(answer);
+   if (ballPredict <= 4) {
+     answer = "very positive";
+   } else if (ballPredict <= 9) {
+     answer = "positive";
+   } else if (ballPredict <= 14) {
+     answer = "negative";
+   } else if (ballPredict <= 19) {
+     answer = "very negative";
+   } else answer = "Something broken";
+
+   return answer;
+ }
+
+
+  
 /* 
 ==================================
 ======= TESTS - DO NOT MODIFY =====
@@ -82,12 +127,16 @@ test("whole magic 8 ball sequence", () => {
   expect(consoleLogSpy).toHaveBeenCalledTimes(1);
   expect(consoleLogSpy).toHaveBeenLastCalledWith("The ball has shaken!");
 
-  expect(checkAnswer(answer)).toBeOneOf([
-    "very positive",
+  // expect(checkAnswer(answer)).toBeOneOf([
+  //   "very positive",
+  //   "positive",
+  //   "negative",
+  //   "very negative",
+  // ]);
+  expect(["very positive",
     "positive",
     "negative",
-    "very negative",
-  ]);
+    "very negative"]).toContain(checkAnswer(answer))
 });
 
 test("magic 8 ball returns different values each time", () => {
diff --git a/mandatory/1-syntax-errors.js b/mandatory/1-syntax-errors.js
index a10cc9ac2..19e701d88 100644
--- a/mandatory/1-syntax-errors.js
+++ b/mandatory/1-syntax-errors.js
@@ -1,16 +1,18 @@
 // There are syntax errors in this code - can you fix it to pass the tests?
 
-function addNumbers(a b c) {
+function addNumbers(a, b, c) {
   return a + b + c;
 }
 
-function introduceMe(name, age)
-  return "Hello, my name is " + name "and I am " age + "years old";
+function introduceMe(name, age){
+  return "Hello, my name is " + name + " and I am " + age + " years old";
+}
+
 
 function getTotal(a, b) {
-  total = a ++ b;
+  total = a + b;
 
-  return "The total is total";
+  return "The total is " +total;
 }
 
 /* 
diff --git a/mandatory/2-logic-error.js b/mandatory/2-logic-error.js
index 9cca7603b..4f41a4e4f 100644
--- a/mandatory/2-logic-error.js
+++ b/mandatory/2-logic-error.js
@@ -1,16 +1,22 @@
 // The syntax for this function is valid but it has an error, find it and fix it.
 
 function trimWord(word) {
-  return wordtrim();
+  
+  return word.trim();
 }
+word = "  CodeYourFuture  ";
+word = " CodeYourFuture teaches coding     ";
 
 function getStringLength(word) {
-  return "word".length();
+ 
+  return word.length;
 }
+ word = getStringLength("A wild sentence appeared!");
+ word = getStringLength("Turtle"); ;
 
 function multiply(a, b, c) {
-  a * b * c;
-  return;
+ const result= a * b * c;
+  return result;
 }
 
 /* 
diff --git a/mandatory/3-function-output.js b/mandatory/3-function-output.js
index 5a953ba60..b113cbd07 100644
--- a/mandatory/3-function-output.js
+++ b/mandatory/3-function-output.js
@@ -1,17 +1,24 @@
 // Add comments to explain what this function does. You're meant to use Google!
+
+/* This function creat an integer random number(by multiplying decimal random number by ten)*/
 function getRandomNumber() {
   return Math.random() * 10;
 }
 
 // Add comments to explain what this function does. You're meant to use Google!
+
+/*This function concat two words which will be pass to the function as an argument
+for example if word1="ali" and word="reza" the result of this function will be "alireza"*/
 function combine2Words(word1, word2) {
   return word1.concat(word2);
 }
 
 function concatenate(firstWord, secondWord, thirdWord) {
-  // Write the body of this function to concatenate three words together.
-  // Look at the test case below to understand what this function is expected to return.
+  return firstWord + " " + secondWord + " " + thirdWord;
 }
+firstWord="code";
+secondWord="your";
+thirdWord="future";
 
 /* 
 ===================================================
diff --git a/mandatory/4-tax.js b/mandatory/4-tax.js
index ba77c7ae2..5e8fda32a 100644
--- a/mandatory/4-tax.js
+++ b/mandatory/4-tax.js
@@ -4,8 +4,13 @@
   A business requires a program that calculates how much the price of a product is including sales tax
   Sales tax is 20% of the price of the product.
 */
+ 
+ 
 
-function calculateSalesTax() {}
+function calculateSalesTax(price) {
+  const saleTax = (price * 20) / 100;
+  return price + saleTax;
+}
 
 /*
   CURRENCY FORMATTING
@@ -17,7 +22,10 @@ function calculateSalesTax() {}
   Remember that the prices must include the sales tax (hint: you already wrote a function for this!)
 */
 
-function addTaxAndFormatCurrency() {}
+function addTaxAndFormatCurrency(price) {
+ 
+  return  `£${calculateSalesTax(price).toFixed(2)}`;
+}
 
 /* 
 ===================================================