15% off $200 = $170. You save $30.
Equation: $200 − (15% × $200) = $200 − $30 = $170.
Another way to read it: you pay 85% of the original price — that's $170.
$170. The discount is $30 and the final price you pay is $170.
You pay $170 (before tax). That's $200 minus a $30 discount.