An item is regularly priced at $72. dan bought it at a discount of 20% off regular price.

 $57.60

Step-by-step explanation: The formula for discount price is:

72-(72*.20) = 57.60

However you can factor out the 72:

72(1.0-0.20)=57.60 the answer would then just be 72(.80) = 57.60

If you need to do it quickly just think "if i took 20% off of 100% i'm left with 80% so this item costs 80% of the regular price"