calculating field based on same name from other field

[LoffKat]

Hi. This is probably so easy, but i'm just boggled right now. I have 2 tables, one for daily input and one for totals. the first table have event name, event date, cost per day per department etc... the second table has profit and totals. the department total field in the totals table needs to calculate the sum from cost per day per department when the event name is the same (some events run multiple days so i need to calculate the total per event). what is the easiest way to do this?