Pumps A, B, and C operate at their respective constant rates. Pumps A and B, perating 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?