IBPS PO RRB PO Prelims 5 Aug 2023 Shift 3 Paper

Two pipes A and B can fill a cistern in 15 hours and 20 hours respectively. A tap can empty the full cistern in 10 hours. All the three taps were open for 4 hours, when it was realized that the emptying tap had been left open then It was then closed. How many hours more would it take for the cistern to be filled?