Add/Subtract AND Check/Uncheck Variables with a checklist

I'm trying to create an exercise where the learner can check and uncheck items on a checklist while adding and subtracting from a total sum. There are numbers associated with each checkbox so if they check the box, they should see a checkmark and their total number increase and if they uncheck, their total number decrease. Can someone help me with the variables to include so the learner can check and uncheck as many times as they want with the sum adding/subtracting? I have read various discussions and viewed youtube videos and haven't found the solution I was looking for. I posted the file and many thanks in advance for your help! 

3 Replies