Center Of Mass

Ball \(A\) of mass 1 kg moving along a straight line with a velocity of \(4 \mathrm{~ms}^{-1}\) hits another ball \(B\) of mass 3 kg which is at rest. After collision, they stick together and move with the same velocity along the same straight line. If the time of impact of the collision is 0.1 s then the force exerted on \(B\) is