From a container, 6 liters milk was drawn out and was replaced by water. Again 6 liters of mixture was drawn out and was replaced by the water. Thus the quantity of milk and water in the container after these two operations is 9:16. The quantity of mixture is:

Let quantity of mixture be x liters.

Suppose a container contains x units of liquid from which y units are taken out and replaced by Water. After operations , the quantity of pure liquid =  $x1-\frac{y}{x}n$ units, Where n = no of operations . 

So, Quantity of Milk =  $x1-\frac{6}{x}2$  

Given that, Milk : Water = 9 : 16 

=> Milk : (Milk + Water) = 9 : (9+16)

=> Milk : Mixture = 9 : 25 

 Therefore,  $\frac{x1-\frac{6}{x}2}{x}=\frac{9}{25}$

=> x = 15 liters