Answer & Explanation:
use the principle of conservation of momentum
take right as positive and left as negative
momentum is the product of mass and velocity
(4 x 8) + (6 x -2) = (4 x -4) + (6 x Y)
32 - 12 = -16 + 6Y
20 + 16 = 6Y
Y = 6m/s
Final answer the velocity of the 6 Kg ball is 6m/s