In the circle given below $\angle{PQR}=100^{\circ}$, where $P, Q$ and $R$ are points on a circle with centre $O.$ Then $\angle{OPR}=$

Question

$\begin{array}{1 1} (a)\; 10^{\circ} \\ (b)\; 15^{\circ} \\ (c)\; 20^{\circ} \\ (d)\; 25^{\circ} \end{array}$