Conside the poset ({2,4,6,7, 9, 12, 18, 27, 36, 48, 60, 72}, |), with the indicated integers and the divides relation. Find the following if they exist; if they do not exist explain why.

a.) maximal and minimal elements

b.) greatest and least elements

c.) least upper bound of {2, 12}

d.) greatest lower bound of {60; 72}