In a mixture of milk and water, there is only 26% water. After replacing the mixture with 7 liters of pure milk , the percentage of milk in the mixture become 76%. The quantity of mixture is:

         Milk             Water 

         74%             26%        (initially) 

         76%             24%        ( after replacement) 

  Left amount = Initial amount  $1-\frac{replaced amount}{total amount}$ 

   24  = 26 $1-\frac{7}{k}$

=> k = 91