Read the passage below and solve the questions based on it.
There are infinite pipes attached to a very big tank. Pipes are numbered like P1, P2, P3…and so on. Its also known that efficiency of every subsequent pipe is half the efficiency of earlier pipe, i.e., the efficiency of P2 pipe is half the efficiency of P1 pipe and so on. However, in case of P1pipe, this rule is not true since there is no earlier pipe. When all the pipes are working together, tank gets filled in 2 h.
What time will P4 take to fill the tank working alone?