The solution to this question is not given on the solutions sheet and I'm stuck. Letting the initial direction of travel of B be positive, I have -3mu=2mv_1+mv_2, where v_1 and v_2 are the velocities of A and B respectively, using conservation of momentum. I also have (v_1+v_2)/-u = e, which leads to v_1=(e-3)u and v_2=(3-2e)u. The problem is that I'm certain v_2 should be negative. But to reiterate my main point, the sheet gives no answers for this question