Pipes A and B can fill a tank in 10 hours and 40 hours respectively. C is an outlet pipe attached to the tank. If all the three pipes are opened simultaneously, it takes 80 minutes more time than A and B together takes to fill the tank. If A and B kept open for 7 hours and closed and then C opened. How much time will C take to empty the tank :
1
49 hours
2
38.5 hours
3
42 hours
4
45.5 hours