For this chain-of-thought reasoning and answer, what was the question?
A + B = 1/20 + 1/15 = 7/60
A + C = 1/20 + 1/12 = 8/60
7/60 + 8/60 = 15/60 = 1/4
4 days * 2 = 8 days
 A: (B)
Q: A can do a piece of work in 20 days. B in 15 days A and C in 12 days. In how many days can A finish the work if he is assisted by B on one day and C on the next, alternately?
Options:
(A) 2 days
(B) 8 days
(C) 6 days
(D) 8 days
(E) 9 days