Let's go through this step by step:
The salesperson sells the car for 25% more than the auction price, which is $15,800 + $15,800 * 25% = $19,750. This is the markup price.
The salesperson gets a 25% commission on the difference between the markup price and the original price.
The difference between the markup and the original is $19,750 - $15,800 = $3,950.
25% of this amount is $987.50