Pipes A and B can fill a tank in 36 hours and 48 hours, respectively. Both pipes are opened together for 9 hours and then A is closed. Pipe B alone will fill the remaining part of the tank now in:

27 hours

A+ = 36 hrs, B+ = 48 hrs,

⇒ A + B were opened for 9 hrs and then A was closed = (4 + 3) x 9 = 7 x 9 = 63 units,

⇒ Remaining units = 144 - 63 = 81 units,

⇒ Time required by B to complete fill the remaining part of the tank = \(\frac{81}{3}\) = 27 hours.