25% off $150 = $112.50. You save $37.50.
Equation: $150 − (25% × $150) = $150 − $37.50 = $112.50.
Another way to read it: you pay 75% of the original price — that's $112.50.
$112.50. The discount is $37.50 and the final price you pay is $112.50.
You pay $112.50 (before tax). That's $150 minus a $37.50 discount.