Calculating days between dates provides you with in-depth training on Business. Taught by Curt Frye as part of the Excel 2013 Power Shortcuts
That's what I am doing here. Despite my best efforts (and the efforts of many folks on BOB) I have never seen a single simple formula that would properly return all of the correct values for the "extra days" portion of this challenge. Since it's easy enough to calculate all of the answers, that's what I have done. I know the answer to all 49 possible cases. The nasty-looking formula used above is using the day number and the number of days and calculating.