An iron-carbon alloy initially containing 0.230wt%C is exposed to an oxygen-rich and virtually carbon-free atmosphere at 1090C. Under these circumstances the carbondiffuses 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 0.173w% after a 7 h treatment? The value of D at 1090C is 4.11011m2/5