of oven with $A=1m^2$ as in Fig. $1$ consists of three materials, and $k_C=50\frac{W}{m}K$ with thickness, $L_A=0\mathrm{.}3m,L_B=0\mathrm{.}15m$ and face temperature $T1=900K$ and the outer surface temperature temperature of $T_{}=1100K,h=25\frac{W}{m^2}*K.$ Determine $k_B$ and