SOLVED Basic Math Program BACK AGAIN :(

[joefox]

Hello
I have a program that i need to be able to figure out the tax rate, and then find out how much tax is owed to the customer.

There are a few tricks when doing this, there are many different shipping rates, that go from 3.95 to 4.95 5.95 etc.
So what I wanted to do was enter information from the invoice and have it automaticly caluclated.

Now this is the tricky part, if the customer ordered say 3 parts, i wanted to be able to find out the tax, then have another box where i could put in the price of the part(if they only returned 1 part instead of the whole order), and then have it figure out the tax on just that part.

Here is some of the data on the invoice:

Tax Amount .68
Sales Amount 4.49
Invioce Amount 9.12

So the first thing i need the to figure out is how to i figure out what percentage of tax was charged, then have that tax amount * it self by all the different shipping rates.
Then have another box where i can put in a single part price, and hit calcuate and get the tax on just that part.

Thanks for the help!