Adding total of a series of numeric questions?

I apologize if my question has already been answered elsewhere - it it has, I wasn't able to find it! 

I've created an 8 question quiz which has end users inputting numerical values. All questions are set up as numeric, with an acceptable range of data indicated. I'd like to add the sum of all input values on a results slide, but I'm a bit stumped on how to do this. I've got to assume it's possible since Storyline 2 can do pretty much anything. Many thanks for any advice/direction you can offer me.