Urgent Help!

I have recently joined a company where they're running a website coded in asp.
I did not create this website, but I know asp quite well.

I am after a piece of code to help sort out a problem with the website.

This is a car warranty website so bare with me while I'll explain what happens.

You type in mileage, year and model.
You select a 4 x 4 option or a 2.7 (extra's)

you select a plan and term. When you get to the last page to print, if you click back the website automatically adds the extras in again.
So it's adding the 4 x 4 or 2.7 engine again.

Is there any coding that can help me stop this, because a lot of people click back and get charged double. can anyone help me?
email me @ jamie.english@cox-internet.com

I would suggest you clear the values on the page where they select all these options. i.e, you should clear these values when the form loads.

Examples:
var1 = "";
var2 = 0;

Alternatively, you may clear the values after they have been added or used in some way. that means somewhere at the end the code.