A $3\mathrm{.}0-$cm diameter sphere is maintained at $900$C and has an emissivity

of $0\mathrm{.}6.$ It is enclosed by another sphere having a diameter of $9\mathrm{.}0$ cm with

an emissivity of $0\mathrm{.}3$ on both its inside and its outside. Both spheres are

enclosed in a large room at $30$C$.($a$.)$ Calculate the heat lost by the small

$($inner$)$ sphere. $($The answer is about $130$ W$.)($b$.)$ Compute the

temperature of the outer sphere. $($The answer is about $750$ K$.)$