I'm going to assume you set up the problem correctly because I can't make sense out of the question.

First you need to replace ALL x's in the second equation:

Thus y = 12 or y = -9. This means that x = 11 or x = -10 respectively.

So your solutions are: (x, y) = (11, 12) or (x, y) = (-10, -9).

-Dan