An iron-carbon alloy initially containing 0.337wt%C is exposed to an oxygen-rich and virtually carbon-free atmosphere at 1050C. 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 0.0wt%C. At what position will the carbon concentration be 0.253 wt % after a 5 h treatment? The value of D at 1050C is 2.71011m2/s