An 800 Kg Car Moving at 4 M/sec to the Right

Multiple Choice

An 800 kg car moving at 4 m/sec to the right strikes a 400 kg car moving to the left. If the cars stick together and stop moving right after the collision, what was the velocity of the 400 kg car?

A) It was stationary
B) 2 m/sec to the left
C) 8 m/sec to the left
D) 4 m/sec to the left