A water tank can be lled by pipe A and B in 2 hours and 3 hours respectively. Now, both pipes are turned on together. They will be turned off until the tank is lled up to 1/6 full. a) How long do they take to ll up to 1/6 full together? (3 marks) b) If the third pipe C is added and all three pipes now turned on together, it takes 50 minutes to ll up the tank. How long does pipe C take to ll up the tank alone