Correct option is (d) 5 km/hr
We can write three-quarters of a kilometre as 750 metres and \(11 \frac 14\) minutes as 675 seconds.
Rate upstream is:
\(\frac{750}{675} = \frac{10}9\) m/sec.
Rate downstream is:
\(\frac{750}{450} = \frac 53\) m/sec
Therefore, rate in still water is:
Now, we convert m/sec into km/hr. as follows:
\(\frac{25}{18} \times \frac{18}5 = \) 5 km/hr.
Hence, the speed of the man in still water 5 km/hr.
