air at standard conditions enters the compressor at a rate of 15 ft3 /s. it leaves at the tank through a 2-in. diameter pipe with a density of 0.0035 slugs/ft3 and a uniform speed of 700 ft/s. (a) determine the rate (slugs/s) at which the mass of air in the tank is increasing or decreasing. (b) determine the average time rate of change of air density within the tank.