If A, B and C together can finish a piece of work in 4 days. A alone in 12 days and B in 18 days, then C alone can do it in?  Choose the correct choice from the following answers.
A) 20  B) 21  C) 30  D) 9  E) 7
C = 1/4 - 1/12 â€“ 1/18 = 1/9 =&gt; 9 days   ANSWER 9
<result>D</result>
If A, B and C together can finish a piece of work in 4 days. A alone in 12 days and B in 18 days, then C alone can do it in?