|The problem is that the IF statement puts a "" (empty cell) in M4 if here is no late fee due. When you try to perform a mathematical operation with that cell, you get the #VALUE error.|
Try this one. I've replaced the "" with a 0. I also replaced the "$15" with just 15 so that everything will be numbers.
BTW... you should select the formula and use Tools...Formula Auditing...Evaluate Formula to single step through the formula with various dates and amounts in the cells. This will help you understand how the formula works. Then you should be able to impress your teacher. :)