Rectangular ducts are used in a building's ventilation system. At a certain junction, two ducts branch off from the main supply duct and carry air to rooms where they discharge at atmospheric pressure. The first branch (40 cm x 70 cm) is 60 m long and carries a volume flow rate of 10 m/min. What is the maximum length of the second branch (30 m * 30 cm) if its volume flow rate is at least 25% of that in the larger branch? Air: density = 1.2kg / (m ^ 3) and v= 1.5 x10^-5 m^2/sec