A 10t wagon moving at 4m/s strikes a 20t wagon moving at 2.5m/s in the same direction. After collision, the 10t wagon travels backwards at 3.6m/s. Find the velocity of the 20t wagon immediately after

A 10t wagon moving at 4m/s strikes a 20t wagon moving at 2.5m/s in the same direction. After collision, the 10t wagon travels backwards at 3.6m/s. Find the velocity of the 20t wagon immediately after impact.