Solve 8x + 9y = 3 and x + y = 0.

We have 8x + 9y = 3 [1] and x + y = 0 [2].We can make x or y the subject. Take y as subject we have y = -x [3].We substitute [3] into [1] and get 8x - 9x = 3 --> -x = 3 --> x = -3.Substituting x = -3 into [2] we get -3 + y = 0 --> y = 3.Final answer: x = -3 and y = 3.