A does half as much work as B in three-fourth of the time. If together they take 18 days to complete the work, how much time shall B take to do it

A. 30 days   
B. 40 days
C. 35 days   
D. none of these
Answer:     A

Explanation:     

Suppose B takes x dáys to do the work.
A takes (2*(3/4)*x) = 3x/2 days to do it.
(A+B)s 1 days work= 1/18
1/x + 2/3x = 1/18 or x = 30.