products options and percentage calculation problem

This is the product I have the problem with



[url]http://clients.mjmni.com/EPS/index.php?dispatch=products.view&product_id=1[/url]





If i select 500 business cards the total is £80, if i add the lamination option i want it to add £8 (10%). Instead CS Cart will only add £5.70 (10% of the original base price of £57.00) no matter what quantity I chose it only adds £5.70.



Another example: if i select 5000 as a quantity (new total=£210) I would want CS Cart to add £21 to the order if lamination is selected, not £5.70!!



How can I make CS Cart calculate the 10% additional cost for the lamination option based upon what is selected in the Quantity option?