Forces and equilibrium — practice question

The diagram shows a particle $A$, with mass $1.2\,\text{kg}$, resting on a plane inclined at $40^\circ$ to the horizontal, and a particle $B$, with mass $1.6\,\text{kg}$, resting on a plane inclined at $50^\circ$ to the horizontal. The particles are joined by a light inextensible string that passes over a small smooth pulley $P$ fixed at the top of the planes. The sections $AP$ and $BP$ of the string are taut and run parallel to the lines of greatest slope of the two planes. Both planes are rough, and the coefficient of friction between each particle and its plane is the same, $\mu$.