Discount Condition in contract

Hi Experts,

Here we have a scenario like below:

For Contract they wanted to give some discount on Basic Rent :

Example :

Conditions:

10-Basic Rent  as 100

20-Discount as 5 %

30-Final Price should be calculated like (100-(100*5%)) and display as 95

so that any charges  I wanted to charge to customer this condition 30(Final Price) as a base

and also If we wanted to charge this 95 in different payments like below with different dates and system should check the total value should not exceed the condition 30-Final Price.

1.Payment 1- 25%

2.Payment 2-40%

3.Payment 3-35%

Please throw some light on this.

Thanks in Advance.

Regards,

Murali