coldfusion logic help

I need help coming up with the logic.

I have 2 classess that been purchased on the payment plan. (the payment plan options are: 4,6 ,9 payments plan).

Let say that course 1 was purchased on 4 payment plan option. The course is consists of 1 theoretical part and 7 practical .

When payment 1 is made no practical parts are released,
when payment 2 is posted 2 practical parts get open up
when payment 3 is posted 2 more practical parts open up
when payment 4 is posted 3 more  practical parts open up

Let say that course 2 was purchased on 4 payment plan option. The course is consists of 1 theoretical part and 3 practical .

When payment 1 is made no practical parts are released,
when payment 2 is posted 1 practical parts get open up
when payment 3 is posted 1 more practical parts open up
when payment 4 is posted 1 more  practical parts open up

Let say that course 3 was purchased on 6 payment plan option. The course is consists of 1 theoretical part and 7 practical .

When payment 1 is made no practical parts are released,
when payment 2 is posted 1 practical parts get open up
when payment 3 is posted 1 more practical parts open up
when payment 4 is posted 1 more  practical parts open up
when payment 5 is posted 2 more  practical parts open up
when payment 6  is posted 2 more  practical parts open up


and so on