Step 4: Compare the correct formula to the other options provided in the problem. For example, the formula 'Net Purchases = Sales - Cost of Goods Sold' is incorrect because it relates to sales activity, not purchases. Similarly, 'Net Purchases = Beginning Inventory + Purchases - Ending Inventory' is incorrect because it calculates inventory changes, not net purchases. Lastly, 'Net Purchases = Purchases - Freight-In + Purchase Discounts' is incorrect because it excludes Freight-In and misplaces Purchase Discounts.