Question

A driver applies the brakes and slows from 35 m/s to 5 m/s. This takes place over 250 m. How long does it take.

Answer 1

The distance

$$d=\frac{v_i+v_f}{2}t$$

The time of braking

$$t=\frac{2d}{v_i+v_f}=\frac{2\times 250\:\rm{m}}{(35+5)\:\rm{m/s}}=12.5\:\rm{s}$$