The salary of Anup is 30% more than that of Barun. Find what percentage is the salary of Barun less than that of Anup?

Let the salary of Barun be $100$.
Then, the salary of Anup is:

$$100+30\%\text{ of }100=130$$

The difference in their salaries is $30$.
Percentage by which Barun's salary is less than Anup's salary:

$$\left(\frac{30}{130}\right)\times 100=\frac{300}{13}\approx 23.07\%$$