Rachel had to complete w pages of math homework, x pages of reading homework and y more pages of biology homework. How many pages of math and biology homework did she have to complete?
First, we need to know how many pages of math and biology homework Rachel had to complete. 

We are given that Rachel had to complete w pages of math homework, x pages of reading homework, and y more pages of biology homework. 

We want to know how many pages of math and biology homework Rachel had to complete. 

We can create the equation w + y = math and x + y = biology.