Answer:
15.6m/s
Explanation:
V1=
because the derivate of the position is the velocity
V1=12t+3
V2=20+
-8t because the integral of the acceleration is the velocity
V2=
V1=V2 to see when the velocities of particles match
12t+3=20-4t^2
4t^2+12t-17=0 we resolve this with 
and we take the positif root
t=1.05 sec
if we evaluate the velocity (V1 or V2) the result is 15.6m/s
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