Summing 3 variables in Real-Time

I have created a series of 3 sliders that auto calculate how much a fitness club will make depending on how many memberships of each category.  It's working great as shown here:

However, at the bottom, I need it to sum the 3 values shown in each of the 3 sliders in real time.  If it was excel, it would simply be a SUM expression adding together those 3 values.  But I can't get it to work for the life of me.   

Any help would be greatly appreciated.

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