Two pipes, when working one at a time, can fill a cistern in 3 hours and 4 hours, respectively while a third pipe can drain the cistern empty in 8 hours. All the three pipes were opened together when the cistern was 1/12 full. How long did it take for the cistern to be completely full?
1
2 hours
2
1 hour 45 minutes
3
2 hour 11 minutes
4
2 hour 10 minutes