Three pipes A, B and C can fill a tank in 6 hours. After working at it together for 2 hours, C is closed and A and B can fill the remaining part in 9 hours. How many hours will take C alone to fill the tank?	Choose the correct choice from the following options
A) 23/2	B) 41/3	C) 49/4	D) 54/5	E) 63/6
The rate of A+B+C is 1/6 of the tank per hour.   After 2 hours, the tank is 1/3 full.   The rate of A+B is 2/3 * 1/9 = 2/27 of a tank per hour.   The rate of C is 1/6 - 2/27 = 5/54   C can fill the tank in 54/5 hours.   The answer is 54/5.
<result>D</result>
Three pipes A, B and C can fill a tank in 6 hours. After working at it together for 2 hours, C is closed and A and B can fill the remaining part in 9 hours. How many hours will take C alone to fill the tank?