A 1200-kg car moving to the right with a speed of collides with a 1500-kg truck and

Question:

A 1200-kg car moving to the right with a speed of collides with a 1500-kg truck and locks bumpers with the truck. Calculate the velocity of the combination after the collision if the truck is initially
(a) At rest,
(b) Moving to the right with a speed of 20 m/s, and
(c) Moving to the left with a speed of 20 m/s.