A and B together can do a piece of work in 6 days and A alone can do it in 11 days. In how many days can B alone can do it?  Choose the correct choice from the following: A) 12 days B) 15 days C) 66 / 5 days D) 21 days E) 22 / 5 days

Rationale: "explanation : a and b can do work 1 / 6 in 1 day a alone can do 1 / 11 work in 1 day b alone can do ( 1 / 6 - 1 / 11 ) = 5 / 66 work in 1 day = > complete work can be done in 66 / 5 days by b answer : option c"
Answer: C