I'm not sure how this can be solved if their is only two velocities?

Two balls are approaching each other head-on. Their velocities are +9.95 and -11.4 m/s.

(a) Determine the velocity of the center of mass of the two balls if they have the same mass.

m/s

(b) Determine the velocity of the center of mass of the two balls if the mass of one ball (v = 9.95 m/s) is twice the mass of the other ball (v = -11.4 m/s).

m/s