Answer:
∠ B = 45°
Step-by-step explanation:
∠ A and ∠ Bare alternate exterior angles and are congruent , then
5x - 15 = 2x + 21 ( subtract 2x from both sides )
3x - 15 = 21 ( add 15 to both sides )
3x = 36 ( divide both sides by 3 )
x = 12
Then
∠ B = 2x + 21 = 2(12) + 21 = 24 + 21 = 45°
