Insects do not have lungs as we do, nor do they breathe through

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 tracheae is 1.73 mm long with a cross-sectional area of 1.52 x 10^-9m². The concentration of oxygen in the air outside the insect is 0.786 kg/m³, and the diffusion constant is 1.70 x 10^-5 m²/s. If the mass per second of oxygen is diffusing through a trachea is 1.96 x 10^-12 kg/s, then find the oxygen concentration at the interior end of the tube.