At one section in an air distribution system, air at 14.7 psi and 100degree F has a velocity of 1200 ft/min a and the duct is 12 in x12 in square. At another section the duct is round with a diameter of 18 inches and the velocity is 900 ft/min. Calculate: a) the density of the air in the round section. b) The weight flow rate of air in lb/hr