Question 57·Hard·Linear Equations in Two Variables

Line $\ell$ has equation $y = mx + 6$, where $m$ is a nonzero constant. Line $\ell$ meets the $x$-axis at point $P$ and the $y$-axis at point $Q$. The line $5x + 3y = 30$ intersects segment $PQ$ at point $R$ such that $PR:RQ = 1:2$.

What is the value of $m$?