Answer
$a). 38.73m/s$
$b). 15.492s$
$c). 19.14m/s$
Work Step by Step
a). $v^{2}=u^{2}+2aS$
$0=u^{2}-2\times 2.5\times 300$
$u=38.73m/s$
b). $t=\frac{v-u}{a}=\frac{0-(38.73)}{-2.5}=15.492s$
c). For the other vehicle, $u=38.73+4.47=43.2m/s$
$v^{2}=43.2^{2}-2\times 2.5\times300$
$v=19.14m/s$