I use FileMakerPro Advanced 10 to manage my small English school. I use a lesson table to record lessons students take. Lessons have a one-lesson rate and a four-lesson-a-month rate. For example, one lesson is 28 dollars but if they take four lessons a month they only pay 98 dollars. At the moment i manually calculate how much each student should pay per month.
What calculation/script should I use to equate lessons with their price and to calculate that if a student takes 4 lessons in a month then the price is different than less than 4?