You want to buy something that costs $98, and it's on sale for 30% off. What is the item's sale price? First, convert the 30% to a real mathematical number. For percents, this is always done by dividing the 30% by 100%, or 30% / 100% = 0.300.
Second, find out what 30% of $98 is. This is the amount of the sale discount. This is always found by mulitplying 0.300 by the item's cost $98, like this:
0.300 x $98 = $29.40. So for this sale, you'll save $29.40 on this item.