The equation that is helpful to us in determining the speed of the car prior to braking is shown below,
Vi² = Vf² + 2ad
where Vi and Vf are initial and final velocities respectively, a is the deceleration, and d is distance. Substituting the known values,
Vi² = 0² + 2(4 m/s²)(85 m)
Vi = 26.08 m/s