Physics question(momentum) 2 kg and 3kg ball?

A 2.0 kg ball and a 3.0 kg ball, each moving at 0.90 m/s, undergo a head-on collision. The lighter ball rebounds opposite its initial direction, with speed 0.90 m/s. Find the post-collision velocity of the heavier ball. keep in mind the initial direction of the lighter ball as positive...whats the velocity? how much mechanical energy got lost in the collision(joules)? help pls...