Question: two side walls and the roof of a furnace are...

Two side walls and the roof of a furnace are maintaind at 600 K and 1200 K respectively, their emissivities being 0.75 and 0.6. The furnace is cubical with sides of 2 m length. The other surfaces are nonabsorbing and reradiating. Determine the heat flow between side walls and the roof,