An FCC iron$-$carbon alloy that initially contained $0\mathrm{.}55\%$C by weight, is exposed to an oxygen$-$rich and virtually carbon$-$free atmosphere at $1325$ K$.$ Under these conditions, carbon diffuses from the inside of the alloy and reacts on the surface with the oxygen of the surrounding atmosphere, keeping the carbon concentration at $0\%$C in the surface positions $($this carbon elimination process is called decarburization$).$ A$)$ How far from the surface will the concentration of carbon be $0\mathrm{.}25\%$C$?$ After $10$ hours of treatment? Data: D$=4\mathrm{.}3-10-11$ m$2/$s B$)$ How long does it take to obtain a concentration of $0\mathrm{.}18\%$C at $0\mathrm{.}5$ mm$?$ C$)$ What is the depth reached after $7$ hours of treatment with a final concentration of $0\mathrm{.}30\%$ C