Explanation:
< PSR = \(\frac{1}{2}\)(180^o) = 90^o (angle substended by a semi-circle)
∴ < TSR = 90^o
< SRT = 90^o - 30^o = 60^o
< PRS = 90^o - 35^o = 55^o
< PRQ = 180 - (60^o + 55^o) = 180 - 115^o = 65^o
< SQR = 35^o(angles in the same segment)
< QSR + < SRQ + < SQR = 180^o
< QSR + 120^o + 35^o = 180^o
< QSR + 155 = 180^o
< QSR = 180^o - 155^o
= 25^o