Answer is C
Let initial quantity of wine =x litre
After a total of 4 operations, quantity of wine
$ x(1-\frac{y}{x})^{n} => x(1-\frac{8}{x})^{4}$
Given that after a total of 4 operations, the ratio of the quantity of wine left in cask to that of water = 16:65
$ \frac{x(1-\frac{8}{x})^{4}}{x} = \frac{16}{81}$
$ (1-\frac{8}{x})^{4} = (\frac{2}{3})^{4}$
$ (1-\frac{8}{x}) = \frac{2}{3}$
$ (\frac{x-8}{x}) = \frac{2}{3}$
3x - 24 = 2x
x = 24