heat transfer

3. A thin disk-shaped wafer (diameter- =30cm ) is maintained at T=100C. The wafer loses heat to the room by convection and radiation from its upper surface while heat is supplied constantly from below. Assuming the surrounding air at 200C and all surrounding surfaces (isothermal/blackbodies) at T=15oC. How much heat (in W) must be supplied to the wafer? h wafer-air =30W/m2K Emissivity of wafer's surface(gray body) =0.85