A child is sitting at the top of a building of height 22 m and drops a ball of mass 0.1 kg. The father of the child, standing on the ground, catches the ball by keeping his hand at a height of 1.5 m from the ground. What is the work done (Wg) by the gravitational force as the ball travels from the child to the father? Find the change in gravitational potential energy (∆U) of the earth-ball system.