How To Do Percents ?

I have a table / Query that when I type in a product name it will pull up the product, specific weight (in grams) and the ingredients that are in it.
(see example below)
I want to be able to type in a percent and have it calculate the percent of the specific weight that is first shown, then show the results.

mycookies:
chocchip specific weight flour (type in percent) (show result)
chochip specific weight salt (type in percent) (show result)
chochip specific weight butter (type in percent) (show result)

I also need this to be able to do the same thing even if there is only one
ingredient for a cookie.

mycookies:
chocchip specific weight flour (type in percent) (show result)

I hope I have explained this good enough...thanks for your help !

(access 2003)