PLz help me! We r doing semester finals and i need to get this lesson finished in 2 hours so i can get my grade up!

Answer:
$84
Step-by-step explanation:
1. If 20% is marked off, then you are selling it for 80%.
2. 455 * 80% = 364
3. Since you are finding the cost markup from 280, then 364-280=84