A 10.0 kg cart and a 15kg cart are locked together with a compressed spring between them. They are then released so that the spring pushes the two carts apart. The 10.0 kg cart is moving at 4.5 m/s afterward. How fast is the 15kg cart moving?

3.0 m/s
2.0 m/s
4.5 m/s
5.0 m/s