5 hours
$latex 60\ km/hr = 60\times \frac{5}{18}\ m/s = \frac{50}{3}\ m/s&s=1$
$latex \therefore\ Speed \propto \frac{1}{Time}&s=1$
$latex => S_{1}\times T_{1} = S_{2}\times T_{2}$
$latex => \frac{50}{3}\times \frac{9}{2} = 15\times T_{2}&s=1$
$latex => 75 = 15\times T_{2}$
$latex => T_{2} = \frac{75}{15} = 5\ hours&s=1$
Hence option [A] is correct answer.