$\begin{align}  & \angle RPS=\angle PRS={{50}^{\circ }}\text{   }\!\!\{\!\!\text{ Base }\angle s\text{ of Isso }\vartriangle \text{ }\!\!\}\!\!\text{ } \\ & \angle RSP={{180}^{\circ }}-\angle RPS-\angle PRS\text{   }\!\!\{\!\!\text{ }\angle s\text{ in a }\vartriangle \text{ }\!\!\}\!\!\text{ } \\ & \angle RSP={{180}^{\circ }}-{{50}^{\circ }}-{{50}^{\circ }}={{80}^{\circ }} \\ & \angle RSP+\angle PQR={{180}^{\circ }}\text{  }\!\!\{\!\!\text{ opp }\angle s\text{ cyclic quad }\!\!\}\!\!\text{ } \\ & \text{8}{{\text{0}}^{\circ }}+\angle PQR={{180}^{\circ }} \\ & \angle PQR={{100}^{\circ }} \\\end{align}$