Question

Two carts with masses of 11.7 kg and 2.5 kg
move in opposite directions on a frictionless
horizontal track with speeds of 6.6 m/s and
3.1 m/s, respectively. The carts stick together
after colliding head-on.
Find their final speed.
Answer in units of m/s

Answer 1

Spamming the board with all these questions under different names (we can see that you're posting from the same computer) won't get you anywhere.

Are you taking a test?

Answer 2

Learn to apply the law of conservation of momentum. It is all you need to solve this problem.