add fees depending on the quantity of the product

Question

I have installed commerce_fees and created custom fees, then created a rule to apply fees on 'order', but what I want to do is to add fees depending on the quantity of the product.

For example I have product A, quantity 1, then the fee will be, for example, $100. then if I change its quantity to 2, the fees should now be $200.

how can I tweak the rule I created to do so?

Thanks!

Please free to ask anything or added information that might help you understand my problem.

EDIT:

so my workaround here is to limit the quantity of product per line to 1, i made this using rules. my problem now is to add the fee for certain product type. example i have in my cart. product A - type a, then product b - type b.. i want my fee to bee only added once, but when there are two instance of type b. the fee will now be added twice.

any hint guys?