A can do a piece of work in 4 days. B can do it in 10 days. With the assistance of C they completed the work in 2 days. Find in how many days can C alone do it?  Choose the correct choice:
A) 22 days	B) 20 / 3 days	C) 67 days	D) 17 / 6 days	E) 18 days

Rationale: "c = 1 / 2 - 1 / 4 - 1 / 10 = 3 / 20 = > 20 / 3 days answer : b"
Answer: B