$(10$ points$)$ A firm's grows margin is the difference between revenue and cost of goods. For cxample if Whole Foods sells a box of cereal for $$8$ and it cast Whole Foods $$5$ to purchase the cercal, then the grows margin on that item is $$8-$$$5=$$$3.$ To be able to compare grows margins scross products and companies, the gross margin is often expressed as peroentage of the sales