Loan Calculator

I am a student of Web Design and I have now an assignment to do but I am having difficulties with the ActionScript3.

I need a Loan Calculator Flash/AS3, containing two sections:
- an input section, where the user can enter their details and select the amount required
- an output section, where the results of the calculation are displayed.

The input section should contain:
- amount of loan
- repayment period
- whether they want to take Loan Repayment Protection - if yes, the cost of payment protection will be 3% for the total loan amount before interest.

The output section should contain:
- personalised message thanking for their enquiry.
- Interest Rate, should be:
1) UK Base Rate = 4.50%
2)Loan between £1,000-£4,000, interest rate = BR + 5.25%pa
£5,000-£19,999, interest rate = BR +4.50%pa
Greater than that, int.rate= BR + 2.75%pa

Please I really need help, part of it I have already done but the repayment protection and interest rate I can not do it.

Thank you