calculator square foot

I have a need for a square foot calculator for Virtuemart running under joomla 1.5 in essence I need them to choose a width, a width fraction, a length, a length fraction and then do the math L x W / 144 x Price so a blind that is a 34.00 x 72.00 should be 34x72=2448 / 144 = 17 x price This is for 1 product entry in virtuemart, I would like it to be installed as a component for virtuemart here is the link to the working calculator under oscommerce which we are phasing out [login to view URL] I need the following drop down boxes Width: Variables will be from 7 to 72 Width Fraction: .00 to .75 Length: variable will be from 12 to 84 Length Fraction: Quantity: