15% off $50 = $42.50. You save $7.50.
Equation: $50 − (15% × $50) = $50 − $7.50 = $42.50.
Another way to read it: you pay 85% of the original price — that's $42.50.
$42.50. The discount is $7.50 and the final price you pay is $42.50.
You pay $42.50 (before tax). That's $50 minus a $7.50 discount.