So Angle 5 = 1x - 7 and angle 2 = -2x + 18. You can work out that angle 1 is the same as angle 5 because corresponding angles are equal. Then you know that angle 1 + angle 2 = 180 because angles on a straight line add to 180. So therefore 1x - 7 -2x + 18 = 180 so -1x + 11 = 180 so -x = 169 so x = -169. Hope this helps :)