If they're referring to the 1996 movie, then it was certainly Joel Coen. Could the answer be misspelled Cohan? Or is there some other Fargo being referenced?
IMDb gives Joel the directing credit and Joel & Ethan the writing credits. Ethan is listed as "director (uncredited)". There are 2 other movies titled "Fargo" but none directed by anyone with a 5-letter last name.
40a is 'theta' which makes your available letters ?T?A? and
believe the answer is 'ETHAN' although Joel Coen was the
director to the best of my knowledge??