Trying to add two columns in Power Query M without requiring a specific name

New to Power Query.

I’m looking for a way to add two columns together by row using Power Query M without requiring a specific name for the column.
The headers are subject to change but always mean the same. (Ex: Dunkin, Dunkin Donuts, DD)

Here is an example of what i’m looking to do, with the “Total” column being the result of the function.

Previously we were attempting something similar to PA1 + PA2, but it thought we were trying to add the words “Floor” and “Backroom” together instead of the rows below it.

Right now it’s working this way:

#”addCol Fixtr Totals” = Table.AddColumn(Source, “Fixtr Total”, each [#”‘Floor'”] + [#”‘Backroom'”]),

but we need to replace the [#”‘Floor'”] with something that will change when the columns are named different.

You can use Expression.Evaluate() and column indexes.

let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Floor", Int64.Type}, {"Backroom", Int64.Type}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Custom",  let
a = Table.ColumnNames(#"Changed Type"){0},
b = Table.ColumnNames(#"Changed Type"){1}
in Expression.Evaluate("each [" & a &"] + [" & b & "]" ))
in
    #"Added Custom"

Add column … custom column … with formula

=Record.FieldValues(_){0}+Record.FieldValues(_){1}

if you have a bunch of columns adjacent to each other you can do

= List.Sum(List.Range(Record.FieldValues(_),xxx,yyy))

and set xxx and yyy based on https://learn.microsoft.com/en-us/powerquery-m/list-range