Mixture and Alligation question bank (Quantitative Aptitude)

In a mixture of milk and water with a total volume of $60$ $L$,the ratio of milk to water is $7:5$. How much water must be added to make the ratio of milk to water equal $(1:1)$? (in $L$)

$A$ mixture of milk and water measures $60 \, ltr$. It contains $20 \%$ water. How many litres of water should be added to it so that water may be $25 \%$ (in $ltr$)?