add fees depending on product quantity

hi! ive been working for this for quite a while now and i would like to ask if anyone knows how to add custom fee per product quantity.. i installed the module commerce_fees, and created a custom fee, then created a rule that add the custom fee.

for example, i have product A quantity 1, so custom fee = $100 so if product A's quantity becomes 2, custom fee should now be $200 but my rules only adds custom fee to the whole order.

thanks for anyone replying.

Posted: Apr 21, 2014