You should have experience with Excel before trying to use formulas to calculate what day of the week the 15th of a given month is, and you have several options to do this.

Q. Is there an easy way to calculate how long in years and months the employees have been working for my company? A. Excel can do that, as long as you’ve listed all the employees in a database. If so, ...

Learn how to calculate the net present value (NPV) of your investment projects using Excel's XNPV function.

The article How to calculate conditional subtotals in an Excel revenue sheet uses simple expressions, a function, and a conditional format to display a daily balance in a revenue sheet.

Learn how to calculate the Simple Interest in Excel either for a single entry or a range or entries, between two dates, using this forumula.

Writing Excel formulas isn't easy if you don't speak the language. Fortunately, at least two sites will translate your request, in English, into Excel code.