A toy gun sitting on a table when the 0.200 kg foam bullet shoots out a 15.0 m/s. What is the velocity of the gun if it has a mass of 1.35 kg

In a game of pool, ball a is moving with a velocity v0 of magnitude v0 = 15 ft/s when it strikes balls b and c, which are at rest and aligned as shown. knowing that after the collision the three balls move in the directions indicated and assuming frictionless surfaces and perfectly elastic impact (that is, conservation of energy), determine the magnitudes of the velocities va, vb, and vc.