You are investigating surface hardening in iron using nitrogen gas. Two 5 mm thick slabs of iron are separately exposed to nitrogen environments at 850°C and 950°C, respectively. Both situations have achieved a steady-state diffusion condition. The concentration of nitrogen at the higher pressure surface at each temperature is 4 kg/m3 . What is the concentration of nitrogen on the lower pressure surface of each slab slab given that the diffusion flux is 9.0 x 10 -8 kg/(m2 *s)?