Answer:
28%
Explanation:
The discounted price was (1.00 - 0.20)($75), or 0.8($75) = $60.
Adding 10% to that results in (1.00 + 0.10)$60, or 0.9($60) = $54, which represents the final price including 10% service fee.
The final price is $54, down from $75. The discount was ($75 - $54), or $21.
This discount, as a fraction of the original price, was
$21
-------- * 100% = 28%
$75