1/. Stage your Excel files in a database
2/. Build a data flow with the calculations, 2-column target table:
map month to date_part(column1,'MM')
map working_days to sum(decode(column2='working',1,0))
group by date_part(column1,'MM')
3/. Buld a 2nd flow to join both inputs on the month column
and map avg_budget to budget/working_days