Quantity I: A vessel contains a mixture of milk and water in the ratio of 7 : 5. If 9 litre of mixture is sold and replaced by same amount of water then the new mixture contain milk and water in the ratio 7 : 9. Find initial amount of water?  Quantity II: A vessel is full of 63 litre of milk. If 9 litre of milk is taken out and replace by water. Further 7 litre of mixture is taken out and replace again with water then find the amount of water at the end?