Let's try with an example.
Suppose you have a gift whose Full Retail Price is $100 and currently there is a promotion running which gives you 10% discount on the Full Retail Price. Thus the Sale Price (or Sales column here) of gift will be
Full Retail Price * (1 - Discount) = Sale Price
i.e. 100 * (1 - 10/100) = $90
In given dataset, we have Sales and Discount (in decimal), and we need to find Full Retail Price. So the calculation will be
Full Retail Price = Sale Price / (1 - Discount)
In the dataset, discount is in decimals instead of percentage. Thus you don't have to do /100 in your calculation
Note, if the discount is 0 then Sales = Full Retail Price.
Hope this helps
Thanks Jim, Rohit..