Given that ∠A and ∠B are supplementary, then
m∠A + m∠B = 180°
Substituting with data:
(5x + 25) + (x + 17) = 180
(5x + x) + (25 + 17) = 180
6x + 42 = 180
6x = 180 - 42
6x = 138
x = 138/6
x = 23
Replacing this result into m∠A equation:
m∠A = (5x + 25)°
m∠A = (5(23) + 25)°
m∠A = (115+ 25)°
m∠A = 140°