11) An angle $A \widehat{O} B$ is trisected by the rays $O P$, $O Q$; the angle $B \widehat{O} C$ (supplementary to $A \widehat{O} B$) is also trisected by the rays $O R, O S$. What is the measure of the angle $Q \widehat{O} R$?

$\begin{array}{llll}\text { (A) } 45^{\circ} & \text { (B) } 60^{\circ} & \text { (C) } 90^{\circ}\end{array}$

(D) it depends on the angle $A \widehat{O} B$

(E) the construction cannot be done.

![](https://cdn.mathpix.com/cropped/2024_04_17_807214d42c092eaa073dg-2.jpg?height=238&width=358&top_left_y=448&top_left_x=1044)
11) The answer is (B). $Q \widehat{O} R=\frac{1}{3} C \widehat{O} B+\frac{1}{3} B \widehat{O} A=\frac{1}{3}(C \widehat{O} A)=\frac{180^{\circ}}{3}=60^{\circ}$.