A man can do a job in 14 days. His father can do the same work in 7 days and his son will take 21 days to complete it. How long will it take to complete the same work, if three of them decide to work together?
1
\(3\frac{9}{11}\) days
2
\(3\frac{7}{11}\) days
3
\(3\frac{1}{2}\) days
4
\(3\frac{1}{3}\) days