after your transpose node you have only string columns.
It seems you read your content from Excel-File. Setup your Excel-Reader with ‘Table contains column names in row number=1’ and ‘Table contains row IDs in column=1’.
If you then transpose your table, you will find your columns in Math Formula.
Unfortunately it doesn’t help me since I have used many other calculations before this and this is one of the cases which I need to calculate in the workflow.