Billiards ball collision

1. The problem statement, all variables and given/known data

2 identical biliards balls collde after a glancing collision determine the speed of the other ball,



2. Relevant equations

MaVa + MbVb = MaVa' + MbVb' ?



3. The attempt at a solution

is this just as simple as the momentum formula before and after, or am I forgetting somthing obvious, because 5cm/s in the other direction dosent make any sense

 

also is there a different formula to use for this when its on an angle, i know momentum before has to equal momentum after as does kinetic energy, mind you its not asking for kinetic, only speed, the balls are the same size so in the momentum formula we can get rid of the mass?, and its obvious its perfectly elastic anyways.