Give the step-by-step reasoning process and then the final answer. Viggo spent $80 on a shirt. He paid the shirt using $20 and $10 bills. If she gave the clerk one more $20 bill than $10 bills, how many $10 bills did he give?
Let x be the number of $10 bills. So, there are (x + 1) $20 bills. Adding the $10 and $20 bills should sum up to $80 so the equation is 10x + 20(x + 1) = 80. Then, distribute 20 to x + 1 so it becomes 10x + 20x + 20 = 80. Combining the like terms on the left side gives 30x + 20 = 80. Then transfer 20 to the right side of the equation, so it becomes 30x = 60. To solve for x, we have 60 / 30 = 2. Therefore, there are 2 $10 bills.
The final answer: 2.