Help me answer

Two particles have positions at time t given by s=4tt2 and s=5t2t3 . Find the velocities v1 and v2 at the instant the accelerations of the two particles are equal.

When i find the accelerations of both i get

a= -2 and a=10-6t

but when i solve for time i get 2.

-2=10-6t

-12=-6t

t=2

An answer of two gives one velocity zero and second velocity 8.

v=4-2(2) V=0

v=10-3(4) v=8

The accelerations of the two cannot be equal if one is zero. Please help