Working together, John, David, and Roger require 2 1/4 hours to complete a certain task, if each of them works at his respective constant rate. If John alone can complete the task in 4 1/2 hours and David alone can complete the task in 9 hours, how many hours would it take Roger to complete the task, working alone? Select:
A) 2 1/3
B) 4 1/2
C) 6 3/4
D) 9
E) 12
(J+9+R)(9/4)=1   J+9+R= 4/9   (2/9 + 1/9 + R) = 4/9   R=1/9   9 hours   Answer: 9
<result>D</result>
Working together, John, David, and Roger require 2 1/4 hours to complete a certain task, if each of them works at his respective constant rate. If John alone can complete the task in 4 1/2 hours and David alone can complete the task in 9 hours, how many hours would it take Roger to complete the task, working alone?