Answers:
x = 12
Angle B = 45 degrees
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Explanation:
Angles A and B are alternate exterior angles.
Due to the parallel lines, alternate exterior angles are congruent
A = B
5x-15 = 2x+21
5x-2x = 21+15
3x = 36
x = 36/3
x = 12
Use this x value to find the measure of angle B
angle B = 2x+21
angle B = 2*12+21
angle B = 24+21
angle B = 45 degrees
As a check,
angle A = 5x-15
angle A = 5*12+15
angle A = 60-15
angle A = 45 degrees
Since A and B are both 45 degrees, this confirms the correct x value
