$729 \ ml$ of a mixture contains milk and water in the ratio $7:2$. How much more water is to be added to get a new mixture containing milk and water in the ratio $7:3$? (in $ml$)

$A$ barrel contains a mixture of wine and water in the ratio $3:1$. How much fraction of the mixture must be drawn off and substituted by water so that the ratio of wine and water in the resultant mixture in the barrel becomes $1:1$?

$A$ mixture of $30 \ L$ contains milk and water in the ratio of $7:3$. How much water should be added to it so that the ratio of milk and water becomes $3:7$? (in $L$)

How many $kg$ of sugar costing ₹ $5.75$ per $kg$ should be mixed with $75 \, kg$ of cheaper sugar costing ₹ $4.50$ per $kg$,so that the mixture is worth ₹ $5.50$ per $kg$?

How much water must be added to a vessel which contains $80$ litres of milk at a cost price of ₹ $3.5/litre$ so that the cost of the milk reduces to ₹ $2/litre$? (in litres)

In what proportion must water be added to spirit to gain $20 \%$ by selling it at the cost price (in $:5$)?