How much money does Mark pay for the desk after the 20% discount is applied?

To determine how much Mark pays for the desk after the 20% discount is applied, we first need to know the original price of the desk. Since it wasn't stated in your question, we can assume a hypothetical original price.

Let's say the original price is $200. To calculate the discount, multiply the original price by the percentage discount expressed as a decimal:

20% as a decimal is 0.20. Therefore, the discount amount is:

$200 × 0.20 = $40.

Now, subtract the discount from the original price to find the sale price:

$200 - $40 = $160.

This calculation shows that after applying the 20% discount, Mark pays $160 for the desk.

The correct answer is therefore based on the final sale price after the discount has been deducted. It reflects both the understanding of percentage calculations and the application of discounts, which are essential skills for managing expenses in various contexts.