Newton's laws of motion — practice question

Block $A$ has mass $3\,\text{kg}$ and is tied to one end of a light inextensible string $S_1$. At the far end of $S_1$ is block $B$ of mass $2\,\text{kg}$, and $B$ is also joined to one end of another light inextensible string $S_2$. The other end of $S_2$ is fastened to a fixed point $O$, so the blocks hang in equilibrium beneath $O$ (see diagram). When $S_2$ breaks, the particles fall. The air resistance on $A$ is $1.6\,\text{N}$ and the air resistance on $B$ is $4\,\text{N}$.