Physics · Heat Transfer

Two very large parallel plates are maintained at uniform temperatures of T1 = 800 K and T2 = 640 K. Their emissivities are 0.2 and 0.5, respectively. What will be the net rate of radiation heat transfer between the two surfaces per unit surface area of the plates? [Assume Stefan-Boltzmann constant σ = 5.67 × 10-8 W/m2·K4 and (800)4 - (640)4 = 2.4 × 1011 K4]