Answer:
b = 15°
Explanation:
The base angles (c = ∠QRP) of ΔQPR are such that the sum of angles of the triangle is 180°. Since the triangle isosceles, the base angles are equal:
2c +60 = 180
2c = 120
c = 60 . . . . . . degrees; the base angle of ΔQPR
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Likewise, the base angle (∠SRP) of ΔSPR is ...
a = (180 -90)/2 = 45 . . . . . degrees
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The measure of angle b is the difference between the larger and smaller base angles:
b = c -a = 60° -45°
b = 15°