How to Sum checkboxes on a seperate slide

This topic has been broached several times but i still have not come across or figured out the best solution for my situation.  Here goes.

I am creating an OJT Practical to be administered by a Trainer or Supervisor on an associate looking to seek certification of an area.  This 'Practical' will be performed using a tablet.

1. I have 2o tasks with each task having 3 checkboxes to click

Yes, No, N.O.  Each check box has a separate variable name.

2. So far I have created 2 triggers for each checkbox, 1st trigger to add points if selected and the 2nd trigger to add zero points if not selected

3. When all 20 tasks have been checked the user will press the SUBMIT button on the slide. 

4. When the next slide appears I want each option, Yes, NO, N.O. to have a sum of each check box from the prior slide.  This will provide dialogue one what the learner performed correctly, and incorrectly thus providing a real time score of the assessment and provide values to upload in our LMS.

5.  My dilemma is where do i sum the check boxes?  I thought I would do this on the SUM, or second slide, when the timeline starts but I do not see how to calculate this using a trigger.  One of the responses to a previous post said, "cb's can be grouped into a button set"  I believe this is what I'm after but i'm still relatively new at this. 

Any further assistance would be greatly appreciated.