A pipe can fill a cistern in 12 hours and a Leak can empty the filled tank in 16 hours. If the efficiency of the pipe is increased by 50% and the efficiency of the Leak is halved, the time taken to fill 90% of the tank is
1
9 hours 30 minutes
2
8 hours 35 minutes
3
8 hours 30 minutes
4
9 hours 36 minutes