A seller is considering how to auction off an item of value. He knows bidders have valuations drawn from a uniform on [0,80][0,80]. At the moment, he has 4 prospective bidders. He is approached by an Auction Success Consultant, who promises that for a fixed fee, he will be able to bring 2 more bidders to the auction (who have valuations alsodrawn from a uniform on [0,80][0,80]).

What is the maximal fee that the seller would agree to, if he is interested only in maximising his expected revenue from the auction?

Please only provide a number and no dollar signs or special characters (e.g. "4.39" rather than "$4.39")