The motors of an electric train can give it a uniform acceleration of $1 \mathrm{~m} \mathrm{~s}^{-2}$ and the brakes can give it a uniform negative acceleration of $3 \mathrm{~m} \mathrm{~s}^{-2}$. The shortest time in which the train can make a trip, starting from a station and stopping at another station that is separated from the starting station by a distance of $1350 \mathrm{~m}$ on straight track, is
(a) $15 \mathrm{~s}$
(b) $30 \mathrm{~s}$
(c) $60 \mathrm{~s}$
(d) $120 \mathrm{~s}$