Creating an Accounts formula for Collection

I really do need help with my problem. I have created a collection program using 3 files: "CASES", "NAMES" and "PAYMENTS". In CASES I maintain the general information on my clients (the following are self explanatory field names), eg fileno, casename, originalamountowed, dateofclaim, balanceowed. In the PAYMENTS the fields are fileno, casename, transactiontype, dateoftransaction, transactionamount, balanceowed. The CASES file will only have one of each fileno. The PAYMENTS file may have many payments relating to each fileno. My problem is creating a formula that uses the originalamountowed from CASES, and the fields from PAYMENTS to record payments in PAYMENTS so that each record in PAYMENTS will show the date a payment was made, the type of transaction (eg cash or check), the amount of the transaction and the balance owed after every transaction. There are other details and variables but I will be able to take it from there. I have a portal in CASES that is supposed to show the following:

Date Transaction Type Amount Balance

HELP!! HELP!! HELP!! :CONFUSED: