First isolate either x or y in x - y = 12: y = x - 12 Substitute x - 12 for y in 27 + 3y = 2x: 27 + 3(x - 12) = 2x 27 + 3x - 36 = 2x -x = -9 x = 9 Substitue 9 for x in x - y = 12 and 27 + 3y = 2x 9 - y = 12 --> y = -3 27 + 3y = 2(9) 27 + 3y = 18 3y = -9 y = -3 So y = -3