A ball of mass m = 4 kg and speed v₁ = 1.2 m/s collides head-on with another ball of 5 kg and speed v₂ = 0.6 m/s. Determine the velocities after the collision (elastic) and the change in linear momentum for the cases:
(a) The two balls move in the same direction
(b) The second ball is moving in the opposite direction
(c) The two balls continue to move together.