Question 135
For a triangle $ABC$ with $\angle ABC = 50^\circ$, points $M$ and $N$ are the midpoints of $AC$ and $BC$, respectively. Point $P$ is the midpoint of $BM$ and point $Q$ is the midpoint of $CM$. It is known that there exists a right triangle with side lengths $CP$, $BQ$ and $MN$. Find the angle between lines $CP$ and $AB$.