An outlet pipe empties a tank which is full in 8 hours. If the inlet pipe is kept open, which lets water in at the rate of 8 litres/min then outlet pipe would take 4 hours longer. Find the capacity of the tank. Choose the correct answer:  A) 8600 litres  B) 200 litres  C) 12800 litres  D) 11520 litres  E) 13200 litres

Rationale: "let the rate of outlet pipe be x liters / hour ; rate of inlet pipe is 8 litres / min , or 8 * 60 = 480 liters / hour ; net outflow rate when both pipes operate would be x - 480 liters / hour . capacity of the tank = x * 8 hours = ( x - 480 ) * ( 8 + 4 ) hours 8 x = ( x - 480 ) * 12 - - > x = 1440 - - > capacity = 8 x = 11520 liters . answer : d ."
Answer: D