Pumps A, B, and C operate at their respective constant rates.  Pumps A and B, operating simultaneously, can fill a certain tank in 6/5 hours; pumps A and C, operating simultaneously, can fill the tank in 3/2  hours; and pumps B and C, operating simultaneously, can fill the tank in 2 hours.  How many hours does it take pumps A, B, and C, operating simultaneously, to fill the tank?