Set up a system of equations:
x+y=25
x-y=7
Use the cancellation method (that's what I call it):
Add the x's together, the y's together, and the constants together to make one big mashed up equation you can solve.
2x=32
x=16
Substitute the number back in to the equation:
x+y=25
16+y=25
y=9
The numbers are 16 and 9. Sorry for the long answer!