Pipe A can fill a tank in 9 hours, pipe B in 18 hours and pipe C in 54 hours. If all the pipes are open,in how many hours will the tank be filled ?	Select.
A) 5.1
B) 5.4
C) 5
D) 5.2
E) 5.5
1/9+1/18+1/54=10/54=1/5.4. so 5.4 hrs   ANSWER:5.4
<result>B</result>
Pipe A can fill a tank in 9 hours, pipe B in 18 hours and pipe C in 54 hours. If all the pipes are open,in how many hours will the tank be filled ?