Energy, work and power — practice question

Particles $A$ and $B$, with masses of $0.35\,\text{kg}$ and $0.15\,\text{kg}$ respectively, are joined by a light inextensible string at their ends. $A$ starts from rest on a smooth horizontal surface, while the string passes over a small smooth pulley fixed at the edge of the surface. $B$ hangs vertically below the pulley, at a height of $h\,\text{m}$ above the floor (see diagram). $A$ is released and the particles move. $B$ reaches the floor and $A$ then arrives at the pulley with a speed of $3\,\text{m s}^{-1}$.