Two balls are approaching each other head-on. Their velocities are +9.30 and -12.1 m/s. Determine the velocity of the center of mass of the two balls for the following conditions. (Use the sign of your answer to indicate the direction.)
(a) They have same mass.
(b) The mass of one ball (v = +9.30 m/s) is two times the mass of the other ball (v = -12.1 m/s).