furnace wall is made up of a steel plate $2\mathrm{.}0$ cm thick, lined on inside with silica $[7$M$]$ bricks $20$ cm thick and on the outside with magnesite bricks $20$ cm thick. The temperature on the inside edge of the wall $8000$C and on the outside of the furnaceis $300$C$.$ Find the amount of heat transmitted through composite wall of the furnacein kilocalories per hour per m$2$ of the furnace wall, surface and the temperature at the interface of steel and magnesite brick. Thermal conductivity for steel, silica brick and magnesite brick are $14\mathrm{.}5,1\mathrm{.}5$ and $4\mathrm{.}5$ kcal$/$hr m $0$C respectively.