OK, so the "MileageRate" field, the Drop Down list, was there as a test for me to get input from an external data source (my other SharePoint list that has the mileage rates) and to be reflected in the calculated value fields column named "Mileage Rate".
This, I was able to get to work so that when a user would select a value from the drop down list, it would be reflected in the calculated value fields.
But I don't want this.
I would like to have radio buttons that specify with or without car allowance, have that pull from the same external data source as above and reflect that in the calculated value fields.
I really hope I'm explaining this right and don't have your head spinning... :)
Does that make sense?