If i remember any mechanics correctly from last year, it's that the resultant mass x velocity should be equal to them before the collision. So, 0.08 x 0.5 = 0.04 and 0.05 x 0 = 0.
0.04 + 0 = 0.08 x 0.1 + 0.05 x W.( I believe you can ignore negatives here as it just dictates direction)
0.04 = 0.008 + 0.05W
0.032 = 0.05W
W = 0.64
So the resulting velocity is, hopefully, 0.64.
(Don't hurt me if this is wrong, I had the best intentions =] )
Good luck, this part of maths is brutal.