Which one of the following shows the best percentage?

Aditya's salary was increased by $40 \%$ and then decreased by $25 \%$. Find the net effect on Aditya's salary.

From a container having pure milk,$20 \%$ is replaced by water and the process is repeated thrice. At the end of the third operation,the milk is: (in $\%$ pure)

The present population of a town is $26010$. It increases annually at the rate of $2\%$. What was the population of the town two years ago?

In an examination,it is required to multiply a number by $7$,but by mistake,a student divides it by $7$. What is the error percentage?

In a certain quantity of ghee, $60 \%$ is pure ghee and $40 \%$ is vanaspati. If $10 \text{ kg}$ of pure ghee is added, the concentration of vanaspati ghee becomes $20 \%$. What was the original quantity (in $\text{ kg}$)?