A thin layer of graphite $($C$)$ is plated onto a thick plate of iron and the couple is held at $1,266$ degrees C for some amount of time. If the approximate depth of penetration at which a there is a $30\%$ concentration of C in the thick plate is $118$m$,$ find the time in seconds The diffusion constants are D$0=8$E$-6$m$2/$s and Qd $=131$kJ$/$mol