SSRS - Calculate a Sum of notEmpty textbox

Question

I'm making a report with SSRS and I would liked to calculate the notEmpty textboxes.

I have a tablix with about 15 columns and 3 of them are either empty or have a "X" as value that I have set in my Query.

Those three columns are like that:

Actually, it's based on time spent inside the store. Under 15 minutes, between 15 and 30 or over 30 min. And the ends, I would like to make a sum in the footer that calculate how many "X" there's in every sections/columns like this:

I know it's not well explained but I don't really know how to see it. I hope someone will be able to help me calculate this.

Thanks

Answer 1

how about

sum(iif(Fields!FieldName.Value ="X",1,0))