[Question]: Jacob can write twice as fast as Nathan. Nathan wrote 25 letters in one hour. How many letters can the two write in 10 hours together?
[Answer]: Since Nathan writes 25 letters in an hour, Jacob writes 25 * 2 = 50 letters in an hour. Together, they write 50 + 25 = 75 letters in an hour,. In 10 hours, they'll write a total of 75 * 10 = 750 letters.
So the answer is 750.

[Question]: Ava planted 9 apple trees in her backyard. That's 3 more than Lily planted in her backyard. How many apple trees did they plant in their backyards collectively?
[Answer]: Lily planted 9 - 3 = 6 apple trees in her backyard. They planted 9 + 6 = 15 apple trees in their backyards collectively.
So the answer is 15.

[Question]: Jay has decided to save money from his paycheck every week. He has decided that he will increase the amount he saves each week by 10 dollars. If he started by saving 20 dollars this week, how much will he have saved in a month from now?
[Answer]:
In one week he will have saved 20 + 10 = 30 dollars. In two weeks he will have saved 30 + 10 = 40 dollars. In three weeks he will have saved 40 + 10 = 50 dollars. At the end of week four, he will have saved 50 + 10 = 60 dollars.
So the answer is 60.