Payment Terms in FICA

Dear All,

          I am hanged up in the configuration of payment terms for fica. Payment terms used by the client is as follows:

if Payment is made:

1.     upto 6th day of calender month then Rebate @ 2% will be allowed,

2.     from 7th day to 9th day then rebate @ (2-X(0.025 per day)) will be allowed,

3.     from 10th to 30th day of calender month then rebate @ (1.925-X(0.033 per day)) will be allowed.

Please help me and how to configure it.

Thanks in advance.