A caterer is agrranging 72 ham sandwiche and 48 pimento cheese sandwiches on serving trays. He would like to arrange the sandwiches so tht each tray has the same number of each kind of sandwich. The number of ham sandwiches on a tray does not need to equal the number of pimento cheese sandwiches on the tray. What is the maximum number of traysthe caterer can use? .