A can do a piece of work in 4 days. B can do it in 9 days. With the assistance of C they completed the work in 2 days. Find in how many days can C alone do it?
Choose one.
A) 22 days  B) 36 / 5 days  C) 67 days  D) 17 / 7 days  E) 18 days

Rationale: "c = 1 / 2 - 1 / 4 - 1 / 9 = 5 / 36 = > 36 / 5 days answer : b"
Answer: B