I have form on table with these fields
i would like to make these transaction for every record
net = month_payments - interest
last_balance = first_balance - net
first_balance = last_balance
please advice me how to do it because i try but not success
First, if the values can be calculated easily, why do you want to store them in the database? It would be better to create a view and do the calculation in the view.
For calculating fields in forms, use formula-items of type "formula"