Hey a little late, but I think for this one you have to use
p= momentum= (mass*velocity)
vf = (p1 + p2)/(m1+m2)
for angle, use tangent.
tan(o) = p2/p1
(o) = tan^-1(p2/p1).
With respect to vector notation, i think you just add and subtract, but for angle use Pythagoras...