8 m/s
Step-by-step explanation:
Using conservation of momentum :-

Where:
m1 = Mass of first vehicle
m2 = Mass of second vehicle
u1 = initial speed of first vehicle
v1 = initial speed of second vehicle
u2 = Final speed of first vehicle
v1 = Final speed of second vehicle
From the received informations:



So

Now divide both sides by m1 :-


Therefore, final answer is 8 m/s