passive intake / exhaust question.....

I was hoping that someone might be able to sahre some knowledge. Have a 2x4x7 tent,400 watt air-cooled light. According to my figures that's 56 cubic feet. First,what is the norm to have the air depleted from the tent per minute.

Then what might be the cfm's for the intake and exhaust. Any decent fans out there that do not sound like an airplane taking off....