4.5 A0.3mby 0.5mrectangular air duct carries a flowof 0 45 m3 s at a density of 2 kg m3. Calculate the mean velocity in the duct. If the duct tapers to 0.15 m by 0.5 m size, determine the mean velocity in this section if the density is 1 5 kg m3 in this section.