30% off $50 = $35. You save $15.
Equation: $50 − (30% × $50) = $50 − $15 = $35.
Another way to read it: you pay 70% of the original price — that's $35.
$35. The discount is $15 and the final price you pay is $35.
You pay $35 (before tax). That's $50 minus a $15 discount.