I am creating a spreadsheet for my dad's check cashing business. I have three
cells: "AMOUNT", "FEE", "CASHED".

He charges an average of .012 or each check. so I enter the formula
"=PRODUCT('AMOUNT*.012) into the "FEE" cell. then I calculated in the
"CASHED" cell "=SUM('AMOUNT'-'FEE') for the total.

Sometimes he doesn't stick to his .012 fee. He wants to be able to put in
the actuall amount he cashed and come up with the fee. Can I not create a
circular reference to the "FEE" cell and have a function that will also
calculate the amount he charge? "FEE"=SUM('AMOUNT'-'CASHED')

How do I do that?