In a 729 litres mixture of milk and water the ratio of milk to water is 7 2 To get a new mixture con...........

milk:water :- 7: 2; Milk:-567, water:-162,

let water added be X.

In new solution Milk:- 567, Water: 162+x,

Total solu:-729+x and ratio is 7:3

simply 7/10(729+x)=567, 

X =81.

Hence, option 3 is the correct answer.