Add up the export values drop down menu selection in a text field

I am creating a timesheet the employee can choose PTO, Unpd, or .  

I have set the export values as follows:

PTO = 8

UnPd = 8

. = 0

I want to sum th PTO selections in 1 text field and sum the Unpd selections in another text field.

Is this possible?  I'm out of room for 2 check boxes for each kind of leave....