Jennifer is twice as old as Peter. The difference between their ages is 15. What is Peters age

Jennifer is twice as old as Peter. The difference between their ages is 15. What is Peters age

Let j be Jennifer's age
Let p be Peter's age

We're given two equations:

1. j = 2p
2. j - p = 15

Substitute equation (1) into equation (2) for j
2p - p = 15

To solve for p, we type this equation into our calculation engine and we get:
p = 15