Momentum — practice question

Small smooth spheres $A$ and $B$, with equal radii and masses of $6\text{ kg}$ and $2\text{ kg}$ respectively, are on a smooth horizontal plane. At the start, $A$ is travelling towards $B$ at speed $5\ \text{m\,s}^{-1}$, while $B$ is travelling towards $A$ at speed $3\ \text{m\,s}^{-1}$. After the collision, both $A$ and $B$ travel in the same direction, and the difference between their speeds is $2\ \text{m\,s}^{-1}$.