If A, B and C together can finish a piece of work in 4 days; A alone can do it in 12 days and B in 18 days, then C alone can do it in :

9 days

The above chart was obtained after following the details of the question:

Efficiency of A + B + C = 9

Efficiency of A = 3

Efficiency of B = 2

Efficiency of C = 9 - (3 + 2) = 4

Days required by C alone to complete the work = \(\frac{36 }{4 }\) = 9 days