At the bottom of a very large vacuum chamber whose walls are at 300 K, a black

Question:

At the bottom of a very large vacuum chamber whose walls are at 300 K, a black panel 0.1 m in diameter is maintained at 77 K. To reduce the heat gain to this panel, a radiation shield of the same diameter D and an emissivity of 0.05 are placed very close to the panel. Calculate the net heat gain to the panel.