Same side interior angles are supplementary, then:
∠A + ∠B = 180°
Replacing with the equations:
(3x - 10) + (x + 82) = 180
(3x + x) + (-10 + 82) = 180
4x + 72 = 180
4x + 72 - 72 = 180 - 72
4x = 108
4x/4 = 108/4
x = 27
Then,
∠A = 3(27) - 10
∠A = 81 - 10
∠A = 71°
