A thin plastic membrane is used to separate helium from a gas stream. Under steady-state conditions the concentration of helium in the membrane is known to be 0.02 and 0.005 kmol/m^3 at the inner and outer surfaces, respectively. If the member is 1mm thick and the binary diffusion coefficient of helium with respect to the plastic is 10^-9 m^2/s, what is the diffusive flux?