15% off $25 = $21.25. You save $3.75.
Equation: $25 − (15% × $25) = $25 − $3.75 = $21.25.
Another way to read it: you pay 85% of the original price — that's $21.25.
$21.25. The discount is $3.75 and the final price you pay is $21.25.
You pay $21.25 (before tax). That's $25 minus a $3.75 discount.