In the diagram, PR is a diameter of the circle PQRS. PST and QRT are…

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