A car starting from rest accelerates at the rate $f$ through a distance $S$, then continues at constant speed for time $t$ and then decelerates at the rate $f/2$ to come to rest. If the total distance traversed is 15 S, then\\
(1) $S = ft$\\
(2) $\mathrm{S} = 1/6\, \mathrm{ft}^2$\\
(3) $\mathrm{S} = 1/2\, \mathrm{ft}^2$\\
(4) None of these