(b) 15 days
(2 Men + 7 Children)'s 1 days' work = \(\frac{1}{4}\)
(4 Men + 4 children)'s 1 days' work = \(\frac{1}{3}\)
\(\Rightarrow\) 2M + 7C = \(\frac{1}{4}\) ............(i)
4M + 4C = \(\frac{1}{3}\) ...............(ii)
Now we can solve the value of man.