Answer: x = 12, ∠B = 45°
Step-by-step explanation:
Angle A and Angle B are alternate exterior angles meaning that they are equal
5x - 15 = 2x + 21
3x - 15 = 21
3x = 36
x = 12
B = 2(12) + 21
B = 24 + 21
B = 45
