An outlet pipe empties a tank which is full in 10 hours. If the inlet pipe is kept open, which lets water in at the rate of 4 litres/min then outlet pipe would take 6 hours longer. Find the capacity of the tank.	Pick one:  A) 8600 litres  B) 6400 litres  C) 12800 litres  D) 11200 litres  E) 13200 litres

Rationale: "let the rate of outlet pipe be x liters / hour ; rate of inlet pipe is 4 litres / min , or 4 * 60 = 240 liters / hour ; net outflow rate when both pipes operate would be x - 240 liters / hour . capacity of the tank = x * 10 hours = ( x - 240 ) * ( 10 + 6 ) hours 10 x = ( x - 240 ) * 16 - - > x = 640 - - > capacity = 10 x = 6400 liters . answer : b ."
Answer: B