Two plane coaxial disks are separated by a distance L

Two plane coaxial disks are separated by a distance L = 0.20 m. The lower disk (A1) is solid with a diameter Do = 0.80 m and a temperature T1 = 300 K. The upper disk (A2), at temperature Tz = 1000 K, has the same outer diameter but is ring-shaped with an inner diameter Di = 0.40 m. Assuming the disks to be blackbodies, calculate the net radiative heat exchange between them.

D, A. T2 A. T D.