help example

[DJ]

Hello everyone.

I need your guidance with some small example, I need to add in
bill some fields like this:

1 to 3 installments of $ 100.00 amount is calculated based on the total bill
2 to 6 installments of $ 75.00
3 to 12 installments of $ 50.00

If I could help is the grateful, sincerely.

Richard Ortiz