Two balls hang from strings of the same length. Ball A, with a mass of 4 kg, is swung back to a point 0.8 m above its equilibrium position. A is released from rest and swings down and hits ball B. After the collision ball A rebounds to a height of 0.2 m above its equilibrium position, and ball B swings up to a height of 0.05 m.

What is the mass of ball B?

1. 4 kg
2. 8 kg
3. 12 kg
4. 16 kg
5. 24 kg
6. None of the above