The space station, Lupus-1, is an enormous spacecraft made up of three identical cylindrical structures that house the living quarters for the crew.   The three cylindrical structures are linked together by a series of tunnels that hold them together and allow the crew to move between cylinders.  Each cylindrical structure contains 12 bedrooms, 7 bathrooms, and several kitchens.  If the entire space station has 72 rooms, how many kitchens are there on the entire space station?
Please reason step by step, and put your final answer within \boxed{}.
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