Work energy & power questions

Two stationary steel balls, A and B, are suspended next to each other by massless, inelastic strings as shown in Diagram 1 below.

Ball A of mass 0,2 kg is displaced through a vertical distance of 0,2 m, as shown in Diagram 2 above. When ball A is released, it collides elastically and head-on with ball B. Ignore the effects of air friction.
4.1. What is meant by an elastic collision? (2)
Immediately after the collision, ball A moves horizontally backwards (to the left). Ball B acquires kinetic energy of 0,12 J and moves horizontally forward (to the right).
Calculate the:
4.2.Kinetic energy of ball A just before it collides with ball B (Use energy principles only.) (3)
4.3.Speed of ball A immediately after the collision (4)
4.4.Magnitude of the impulse on ball A during the collision (5)                      [14]