Scoring - lowering the scale

Hello everyone, 
I've created a questionnaire for mystery shoppers to rate their experience in a restaurant. The more "satisfactory" their answers to the questions, the higher the restaurant's score. For example: "satisfactory" = 6 points, "fairly satisfactory" = 4 points etc. I was able to program a scoring system directly on qualtrics. 
Except that it's possible to select "I don't know" as the answer, which means I'm ignoring the question, and lowering the scale. So I have to calculate the scale by hand using Excel. 
Is it possible to do a double score? For the total obtained and the scale. 
Thanks in advance!