Write a story problem for addition sentence 7 + _ = 9

Solve the story problem.

Story Problem: You have seven apples. Someone gives you a few more apples, but you don't know how many they give you. All you know is that once they leave, you realize that you now have 9 apples total. How many apples did this person give you?

To answer this question, you can guess and check to see that the answer is 2. This is because 7+2 = 9. To use algebra, let x be the number of apples that the person gives you. So we have 7+x = 9 which is the same as x+7 = 9. Subtract 7 from both sides (to keep things balanced) and we end up with

x+7 = 9

x+7-7 = 9-7

x+0 = 2

x = 2

So this is a more formal way to find the answer is 2