Anybody know the answer ?

Answer:
The final speed after collision of the first ball that weighs 4 kg will be 8.5 m/s.
Step-by-step explanation:
M1 = 4
M2 = 2
V1 = 8
V2 = 6
V2f = 5
V1f = ?
Rep. Situation with Momentum formula:
M1*V1+M2*V2 = M1*V1f+M2*V2f
Rearrange:
((M1*V1+M2*V2)-M2*V2f) / M1 = V1f
Calculate:
((44) - 10) / 4 = V1f
V1f = 8.5