An FCC iron-carbon alloy initially containing 0.55 wt% C is exposed to an oxygen-rich and virtually carbon-free atmosphere at 1325 K. Under these circumstances, the carbon diffuses from the alloy and reacts at the surface with the oxygen in the atmosphere -- that is, the carbon concentration at the surface position is maintained essentially at 0 wt% C. This process of carbon depletion is called decarburization. At what position will the carbon concentration be 0.20 wt% after 10 h treatment?