How to Calculate the Increase in KE in a Two-Cart System with Spring Release

[misyg]

Two carts, a blue one with a mass of 350g and a silver one with a mass of 500g, move down a frictionless, level track together at .20 m/s to the right. When the two carts reach the center of the track, the spring on the silver cart is released, and the two carts move apart. The final velocity of the silver cart is .40 m/s to the right. How much does the final KE of the two cart system increase by when the spring is released?

I tried combining the masses and velocity but it just ended badly...please help.

 

[tiny-tim]

hi misyg!

show us your full calculations, and then we'll see what went wrong, and we'll know how to help!