$3.$ Consider a hot yam with surface conditions $(=375,=0\mathrm{.}93)$ enclosed into a large room with the surface temperature of the walls $(=70).$ The hot yam radiates heat uniformly in all directions and to keep it warm, one decides to cover it with a single layer of thin aluminium foil with emissivity of $0\mathrm{.}2.$ Assume the yam I spherical in shape with a diameter of $4\mathrm{.}5$ in and the thin foil forms a spherical shell around the yam. Determine the net rate of radiation loss from the yam a$)$ With the foil assuming the thickness of the foil is negligible b$)$ without the foil