Hey all! Its me again... (Headbang)

My problem this time, is

How do I find the list price when I have these to work with

So its basically organized like this on a chart:

List Price: XThe question is telling me to find the LIST PRICE & AMOUNT OF DISCOUNT. I assume I must first find the LIST PRICE before attempting ROD?

Rate of Discount: $80

Amount of Discount: X

Net Price: $40