Energy, work and power — practice question

Particles $A$ and $B$ have masses of $0.4\,\text{kg}$ and $1.6\,\text{kg}$ respectively. They are connected by a light inextensible string passing over a fixed smooth pulley. Particle $A$ is kept at rest while $B$ hangs freely, with the two vertical sections of the string straight and each particle initially $1.2\,\text{m}$ above the floor (see diagram). $A$ is let go, and the two particles begin to move.