The mathematics department has six committees, each meeting once a month. Howmany different meeting times must be used to ensure that no member is scheduled to attend two meetings at the same time if the committees are C1 = {Arlinghaus, Brand, Zaslavsky}, C2 = {Brand, Lee, Rosen}, C3 = {Arlinghaus, Rosen, Zaslavsky}, C4 = {Lee, Rosen, Zaslavsky}, C5 = {Arlinghaus, Brand}, and C6 = {Brand, Rosen, Zaslavsky}?