A can do a piece of work in 8 days. B can do it in 12 days. With the assistance of C they completed the work in 4 days. Find in how many days can C alone do it?	Choose the most appropriate option:
A) 87 days
B) 20 days
C) 16 days
D) 24 days
E) 36 days

Rationale: "c = 1 / 4 - 1 / 8 - 1 / 12 = 1 / 24 = > 24 days answer : d"
Answer: D