$3\mathrm{.}11$ The wall of a drying oven is constructed by sandwiching an insulation material of thermal conductivity $k=0\mathrm{.}05\frac{W}{m}*K$ between thin metal sheets. The oven air is at $T_{,i}=300C,$ and the corresponding convection coefficient is $h_i=30\frac{W}{m^2}*K.$ The inner wall surface absorbs a radiant flux of $q_{\text{r}\text{a}\text{d}}^{\text{'}\text{'}}=100\frac{W}{m^2}$ from hotter objects