Question

What is b equal to ?

Answer 1

PQ = RQ and <PQR = 60°
Triangle PRQ is equivalent triangle so <QPR = <QRP = <PQR = 60°

PS = RS, and <PSR = 90°, triangle PSR is a right isosceles triangle
So
a = <SRP =  45°
and
b = <QRP - <SRP
b = 60° - 45°
b = 15°

answer
a = 45°
b = 15°