Answer: 14.49 m/s
Explanation: you would have to use kinematic equations to solve for the original speed.
v^2 = v0^2 + 2 (a) (x) where v = 0 since the car stopped
then you would get v0 = sqrt (2(a)(x))
plug in the known values
v0 = sqrt(2(3.50)(30.0))
v0 = 14.49 m/s
So the answer would be 14.49 m/s