TBH a switch / case in this instance is so simple and rudimentary it's hardly more work to copy / paste someone's answer from here than to just look at a tutorial and do it. But if you want a shot at someone helping you, at least post the data types, meaning post the grades and how they average (are certain grades weghted more than others?) otherwise it's just simple number averaging and labeling it "Persons x's grade" which makes it even simpler!
