Pipes A and B can fill a cistern in 3 and 4 hours respectively. Pipe C can empty it in 9 hours. If all the three pipes are opened together, then the tank will be filled in:
1
\(2{2 \over {17}}\) hours
2
5 hours
3
\(3{{2 \over {17}}}\) hours
4
4 hours
5
None of these