Let p=original price. If you buy a product that's 20% off, you're buying it with 20 percent of that price subtracted from that price. For instance, if an item is originally priced at $100 and it has a 10% discount you pay 10% less than $100. Or in other words 100-10%(100)=100-.1(100=100-10=90. So you would pay $90 instead of $100. The same idea applies here, but we don't know the original price, so we let that be our unknown.
Subtract like terms
Divide both sides by .8
So the original price was $225
Check:
$225-20% of 225=225-.2(225)=225-45=180 So our answer checks out.