An iron-carbon alloy initially containing 0.55 wt% C is exposed to an oxygen-rich and virtually carbon-free environment at 1325 K. Under these conditions, the carbon diffuses from the alloy and reacts with oxygen at the surface. Therefore, the surface concentration of carbon is effectively 0 wt% C. The diffusion coefficient for carbon in iron at 1325 K is 4.3 x 10-11 m2/s. At what depth below the surface will the carbon concentration be 0.25 wt% after a 10 hour treatment?