The ratio of efficiency of pipe A, B and C is 5 ∶ 7 ∶ 3. Altogether three pipes fill the tank in 20 hrs. A and B are inlet pipes and C is an outlet pipe. If A and C open for 13 hrs, in how many hours pipe B alone fill the remaining tank?
1
22 hrs
2
25 hrs
3
20 hrs
4
15 hrs