if both of those are in the same part of the question ie both as a) then I would say that you do it by simultaneous equations x + y = -8 --> leave x - 2y = 7 --> multiply by -1 x + y = -8 -x + 2y = -7 add these 3y = -15 --> y = -5 x + -5 = 8 --> x = -3 x - 2(-5) = 7 --> x = -3 x = -3 y = -5 both equations work, so yeah I think this is the right way to do it

to get that answer you use system of equations. which means multiplying by a certain number to get something in common so they cancel out!