Two carts with masses of 13.2 kg and 3.0 kg

Question

move in opposite directions on a frictionless
horizontal track with speeds of 6.8 m/s and
3.5 m/s, respectively. The carts stick together
after colliding head-on.
Find their final speed.
Answer in units of m/s.

Answer 1

M1*V1 + M2*V2 = M1*V + M2*V.
13.2*6.8 + 3*(-3.5) = 13.2V + 3V.
V = ?