I need to generate some calculations but I have no idea where to start or how to do it. This is what I need to do:

Amount Billed: $xxx.xx (This is manually entered)
Insurance Paid: $xxx.xx (This is manually entered)
Member Responsibility $xxx.xx (amount billed - Insurance Paid) ****
Payments Made: $xxx.xx (This is manually entered)
Balance: $xxx.xx (Member Responsibility - Payments Made) ****

How and where do I create these *** calculations?