A chef had w apples and x peaches. After making some pies, he had y apples left. How many apples did he use?
First, we need to find out how many apples the chef had in total. We know that he had w apples and x peaches, and we know that he had y apples left. This means that the total number of apples must be w + y. 

Now, we need to find out how many apples the chef used. To do this, we need to subtract the number of apples left from the total number of apples. We know that the number of apples left is y, so the number of apples used must be w + y - y. 

This means that the chef used w apples.

Therefore, the answer (symbolic expression) is: 

w