How do I combine columns in a table in Looker Studio so that all the data is in one column?

I have the following table. 

julief_0-1717612434612.png

I want to combine the columns Adjusted Area Field 1, 2, and 3 into one combination column and sum the results. If done correctly, the results should look as follows:

julief_2-1717612457791.png

How do I do this in Looker Studio?