Answer:
Angle B = 27°
Explanation:
Since XY is a straight line, all the angle add up to 180°
Let the 90° angle marked by the color yellow be angle c
Given
Angle A = 63°
Angle C = 90°
Therefore
Angle A + Angle B + Angle C = 180°
63 + Angle B + 90 = 180
Angle B = 27°