Set total to radio button

If you would like to populate a Total from a Radio Button selection, please take a look at the following screencast:

http://screencast.com/t/OC7Sy6xX

If I misunderstood the request, please let me know. Thank you.

Worked great!  I did have to do a little dancing around one issue though.  I would like to have a "other" radio button where our "donors" can input what ever number they want. The hidden calculation in the referenced video was great, but it will not calculate a other radio button text field with customer input data.  My work around was to just add more input choices and hope those would suffice for the donor.  Otherwise the screencast show exactly what I was after. Thanks