A. 12 days
B. 15 days
C. 16 days
D. 18 days
A's 2 day's work = (1/20) x 2 = 1/10
(A + B + C)'s 1 day's work = (1/20) + (1/30) + (1/60) = 1/10
Work done in 3 days = (1/10) + (1/10) = 1/5
Now, 1/5 work is done in 3 days
=> Whole work will be done in (3 x 5) = 15 days