The net radiation heat exchange rate in kW/m2 between the two plates is

Question

Two large diffuse gray parallel plates, separated by a small distance, have surface temperatures of 400 K and 300 K. If the emissivities of the surfaces are 0.8 and the Stefan-Boltzmann constant is 5.67´10^–8W/m²K⁴, the net radiation heat exchange rate in kW/m² between the two plates is                                      

      (a) 0.66                                                               (b) 0.79

      (c) 0.99                                                               (d) 3.96