A and B together can do a work in 6 days. If A alone can do it in 15 days. In how many days can B alone do it?  Choose the correct option:  A) 10  B) 99  C) 77  D) 55  E) 21

Rationale: "1 / 6 – 1 / 15 = 1 / 10 = > 10 answer : a"
Answer: A