Two pipes A and B together can fill a tank in 20 hours. Ratio of efficiency A and B is 5 : 4. If both pipe together filled the tank for the first 4 hours, after that pipe B closed and another pipe C is opened and tank filled in another 9 hours. Find pipe C alone can fill the tank in how many hours.

Options

A. A)`(90)/(7)`hours
B. B)`(80)/(5)`hours
C. C)`(180)/(11)`hours
D. D)`(180)/(7)`hours

Answer

C