A cylindrical air duct in an air conditioning system has a length of 5.5 m and a radius of 7.2 × 10-2 m. A fan forces air (η = 1.8 × 10-5 Pa ∙ s) through the duct, so that the air in a room (volume = 280 m3) is replenished every ten minutes. Determine the difference in pressure between the ends of the air duct.