Newton's laws of motion — practice question

Two particles, $A$ and $B$, with masses $0.3\text{ kg}$ and $0.2\text{ kg}$ respectively, are fastened to the two ends of a light inextensible string. $A$ is kept at rest on a rough horizontal table, and the string passes over a small smooth pulley at the table edge. $B$ hangs vertically beneath the pulley. The system is released and $B$ begins to move downwards with acceleration $1.6\text{ m s}^{-2}$.