Momentum — practice question

Particle $A$, with mass $2.5\text{ kg}$, is let go from rest at the top of a smooth plane inclined at an angle of $\sin^{-1}0.2$ to the horizontal. Two seconds later, $A$ collides with particle $B$, of mass $3\text{ kg}$, which is travelling up the line of greatest slope of the plane. Just before the collision, the speed of $B$ is $3.5\text{ m s}^{-1}$. Immediately after the collision, $B$ moves with velocity $0.5\text{ m s}^{-1}$ down the plane.