$\begin{align}  & \angle OPR=\angle OQR={{50}^{\circ }}\text{   } \\ & \text{ }\!\!\{\!\!\text{ }\angle \text{s on the same base and segment }\!\!\}\!\!\text{ } \\ & \text{Consider }\vartriangle POR \\ & \angle OPR+\angle POR+\angle PRO={{180}^{\circ }} \\ & {{50}^{\circ }}+{{110}^{\circ }}+y={{180}^{\circ }} \\ & \angle PRO=y={{20}^{\circ }} \\\end{align}$