If two angles are supplementary, it means that the sum of the angles is 180 degrees. Given that angle A and B are supplementary, it means that
angle A + angle B = 180
From the information given,
angle A = 2x - 6
angle B = x + 12
Thus,
2x - 6 + x + 12 = 180
2x + x = 180 + 6 - 12
3x = 174
x = 174/3
x = 58
