Air enters a tank through an area of 0.2 ft2 with a velocity of 15 ft/s and a density of 0.03 slug/ft3. Air leaves with a velocity of 5 ft/ s and a density equal to that in the tank. The initial density of the air in the tank is 0.02 slug/ft3. The total tank volume is 20 ft3 and the exit area is 0.4 ft2. Find the initial rate of change of density in the tank.