When can do a piece of work in 18 days if he works for 3 days, then what fraction of work is left

A and B can do a piece of work in 18 days: B and C can do it in 24 days while C and A can finish it in 36 days. In how many days can A. B. C finish it. if they all work together?

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$=\frac{4+3+2}{72}$ {LCM $18,24$ and $36=72$}
$=\frac{9}{72}$
$\therefore 2(A+B+C)$'s one day's work $=\frac{1}{8}$

Hence, $A,B$ and $C$'s one day work $=\frac{1}{8\times 2}=\frac{1}{16}$

$\therefore$ $A,B$and $C$ can do the work in $16$ days.