Calculate markup and margin percentages based on cost and selling price.
Markup is the amount added to the cost of a product to determine its selling price. It's calculated as a percentage of the **cost**.
Formula: `Markup = ((Selling Price - Cost) / Cost) * 100`
Gross Profit Margin (or simply margin) is the percentage of revenue that is left after accounting for the cost of goods sold. It's calculated as a percentage of the **selling price**.
Formula: `Margin = ((Selling Price - Cost) / Selling Price) * 100`