$!$

Required information

An electric heater with a total surface area of $0\mathrm{.}25m^2$ and an emissivity of $0\mathrm{.}75$ is in a room where the air has a temperature of $20C$ and the walls are at $10C.$ When the heater consumes $500$ W of electric power, its surface has a steady temperature of $120C.$ Determine the temperature of the heater surface when it consumes $770$ W $.$

Given: $=5\mathrm{.}67{10}^{-8}\frac{W}{m^2}*K^4$

Solve the problem taking radiation into consideration.