Newton's laws of motion — practice question

Particles $P$ and $Q$, each of mass $m\,\text{kg}$, are fastened to the two ends of a light inextensible string. That string passes over a fixed smooth pulley attached to the edge of a rough plane. The plane makes an angle $\alpha$ with the horizontal, where $\tan \alpha = \frac{7}{24}$. Particle $P$ is on the plane and particle $Q$ hangs vertically, as shown in the diagram. The part of the string between $P$ and the pulley is parallel to a line of greatest slope on the plane. The system is in limiting equilibrium.