A 2 kg ball moving at $24 ms^{-1}$ undergoes inelastic head-on collision with a 4 kg ball moving in the opposite direction at $48\;ms^{-1}$. If the coefficient of restitution is $2/3$, their velocities in $ms^{-1}$ after impact are :

Question

\[\begin {array} {1 1} (a)\;-56,-8 & \quad (b)\;-28,-4 \\ (c)\;-14,-2 & \quad (d)\;-7,-1 \end {array}\]