answer these questions for the poset ({2, 4, 6, 9, 12, 18, 27, 36, 48, 60, 72}, |). a) find the maximal elements. b) find the minimal elements. c) is there a greatest element? d) is there a least element? e) find all upper bounds of {2, 9}. f) find the least upper bound of {2, 9}, if it exists. g) find all lower bounds of {60, 72}. h) find the greatest lower bound of {60, 72}, if it exists.