A railroad car with mass of 20000 kg moving at 3 m/s collides and joins with two railroad cars already joined together, each with same mass as the

A railroad car with mass of 20000 kg moving at 3 m/s collides and joins with two railroad cars already joined together, each with same mass as the single car and initially moving in the same direction at 1.20 m/s.a) wat is the speed of the three joined car after the collision?b)What is decrease in kinetic energy during the collision?