Insects do not have lungs as we do, nor do they breathe through their mouths. Instead, they have a system of tiny tubes, called tracheae, through which oxygen diffuses into their bodies. The tracheae begin at the surface of the insect's body and penetrate into the interior. Suppose that a trachea is 1.9 mm long with a cross-sectional area of 2.1 10-9 m2. The concentration of oxygen in the air outside the insect is 0.28 kg/m3, and the diffusion constant is 1.1 10-5 m2/s. If the mass per second of oxygen diffusing through a trachea is 1.7 10-12 kg/s, find the oxygen concentration at the interior end of the tube.