50% off $150 = $75. You save $75.
Equation: $150 − (50% × $150) = $150 − $75 = $75.
Another way to read it: you pay 50% of the original price — that's $75.
$75. The discount is $75 and the final price you pay is $75.
You pay $75 (before tax). That's $150 minus a $75 discount.