How to do Calculations In a Text Box?

[SteveF]

I have a text box with several short sentences that are more or less options in a sales proposal. I want to know if it is possible to calculate the dollar amount in each sentence based on a particular number (square footage).



The text box sentence looks something like:

OPTIONAL: 1/2" Thick Clear Glass adds $300.00 plus tax
Sign:_____________________
OPTIONAL: Starphire Low Iron Glass adds $360.00 plus tax
Sign:_____________________

So if the total square footage is 30 sq. ft., in this case the first option is calculated in a simple formula of 30 x $10 psf = $300.00. The second would be 30 x $12 psf, etc.

How do I make this happen in my MS Word doc?