Price Based On Global Options

Hello all,



I need to change the price computing algorithme in order to do that:

I have two product options: a and b



if a is selected the new price is: Price+a_price

if b is selected the new price become (Price+a_price)b_quantity



The current processor do not handle this kind of dependency, it allows to do that:





if a is selected the new price is: Price+a_price

if b is selected the new price becomes Price
b_quantity+a_price



Any suggestion?



Thank you for your help,

Regards