c$)$ Two very large parallel plates are maintained at uniform temperatures of $T_1=750K$ and $T_2=323K$ and have emissivities ${}_1=0\mathrm{.}3$ and ${}_2=0\mathrm{.}75,$ respectively. Select number of radiation shields to reduce the heat transter rate to $90\%$ of without radiation shield case and when hot flue gas is present between the plates, analyse for possible changes in heat transfer.