Energy, work and power — practice question

Particles $A$ and $B$, whose masses are $0.8\,\text{kg}$ and $1.6\,\text{kg}$, are joined by a light inextensible string. $A$ is on a smooth plane inclined at angle $\theta$ to the horizontal, with $\sin \theta = \frac{3}{5}$. A small smooth pulley $P$ is fixed at the top of the plane, and $B$ hangs freely (see diagram). The part $AP$ of the string is parallel to the line of greatest slope of the plane. The particles are let go from rest while both parts of the string remain taut.