Field needed not showing up for calculation order

I need a difference calculation provided (positive or negative). An amount entered by a form user to calculate the difference. This is the information required on form:

The user would enter the "Advanced Check Amount" and the "Cash owed toreturned" needs to show the difference, be it positive or negative. (Amount1-3  boxes are misc expenses)

Definitely not a pro here, so forgive me if it's something Captain Obvious would know lol.

I've exhausted research options and just want to know if this is possible or not. Thanks for anyone's help.