Form/dropdowns that calculate total into a textarea?
I've got a form with many dropdown boxes - what needs to happen is people select things in the dropdown boxes and a number is calculated at the bottom. Each dropdown box might have something like:
Type of user: * Newbie (1 point)
* Regular (5 points)
* Addict (10 points)
Donation: * $0-$5 (add 10 points)
* $5-$10 (add 20 points)
* $10-$20 (add 25 points)
Time on forum: * 1 week (multiply by 1)
* 1 month (multiply by 2)
* 6 months (multiply by 3)
* 1 year (multiply by 4)
At the bottom of the form there is a "Calculate" button, and a textarea called "total points". What I want to happen is for a number to be calculated when they click on the button, depending on what was chosen in the dropdown box - and the total value comes up in the textarea.
(If it's possible, the button doesn't even need to be there - maybe anytime something is selected in the dropdown box, the total is automatically calculated?)
I'm not sure how I calculate this, or give each dropdown box entry its own value. I realize I can do this in PHP, but it's important that it all happens on the one page.