PLEASE HELP

A 10.0 kg cart and a 15 kg cart are locked together with a compressed spring between them. They are then released so that the spring pushes the two carts apart. The 15 kg cart is moving at 3.0 m/s afterward. How fast is the 10.0 kg cart moving?

A) 3.0 m/s

B) 4.5 m/s

C) 5.0 m/s