Question 58·Hard·Geometry and Trigonometry

Two straight conveyor belts are represented by parallel lines $\ell_1$ and $\ell_2$. Point $P$ lies on $\ell_1$, and points $Q$ and $R$ lie on $\ell_2$. Segments $PQ$ and $PR$ are drawn.

The measure of the angle between $PQ$ and $\ell_1$ (on the interior side between the two parallel lines) is $(3x-20)^\circ$. The measure of $\angle PQR$ is $(2x+10)^\circ$, and the measure of $\angle PRQ$ is $(x+40)^\circ$.

Which choice is the measure of $\angle QPR$?