Three pipes A, B and C are connected to a tank. A and B can completely fill a tank in 6 hours and 8 hours respectively when operated independently. Pipe C can empty the full tank in 12 hours when opened alone.If all three pipes are opened together and pipe C can empty the tank at the rate of 20 litres/
hour, then the capacity of the tank is
a) 40 litres
b) 60 litres
c) 80 litres
d) 90 litres
Regards