Pipes A and B can fill a tank in one hour and two hours respectively while pipe C can empty the filled the tank in one hour and fifteen minutes. A and C are turned on together at 9 a.m. after 2 hours, only A is closed and B is turned on. When will the tank be emptied?
1
12 : 10 p.m.
2
10 : 30 a.m.
3
12 : 20 p.m.
4
11 : 30 a.m.