how to solve elastic collision in two dimensions? please test tomorrow?

[Hong Lee]

For the question they give initial velocity's for both hockey pucks and the final velocity for one of the hockey pucks. One puck is along the y-axis the other is not initially. Also the final velocity for the one given is along the x-axis. They give no masses. Could you just show me the way using the equations on how to solve? Do masses cancel? Thank you