SSC CPO 24 Nov 2020 Shift 1 Paper

Pipes A, B and C can fill an empty tank in (30/7) hours if all the three pipes are opened simultaneously. A and B are filling pipes and C is an emptying pipe. Pipe A can fill the tank in 15 hours and pipe C can empty it in 12 hours. In how long (in hours) can pipe B alone fill the empty tank?