Correct option is (D) \(7\,\frac{1}{2}\) hrs
\(\because\) Time taken to fill a \(50\,l\) of tank = 5 hours
\(\therefore\) Time taken to fill a \(75\,l\) of tank \(=\frac5{50}\times75\;hours\)
\(=\frac{75}{10}\;hours\) = 7.5 hours
= 7 hours + \(\frac12\) hours
= \(7\frac12\) hours