Help With Basic Formula

I am having a problem with something that I think should be pretty basic - but can’t seem to make it happen and can’t find any guidance in the help.

I have a Table with rows and columns. Basically like a time sheet - I will list work done, then in another column, the hours, the rate, and the cost.

What I would like to see is somewhere I can create a running total of the cost column. I have tried using functions including SUM in various formats, (I can’t recall them all), but I can’t seem to get this to work.

I create a new attribute that is a function. Oddly, it creates a new column with the name of the attribute, and then I just get a “1.00” in each cell under that column header.

So I must be doing something completely wrong. Can someone tell me how I can create a row, with a running total (sum) of the amounts above it?

For anyone else trying to figure this out - thanks to Infinity Support, I have the answer: