The base surface of a cubical furnace with a side length of 3 m has an emissivity of 0.80 and is maintained at 500 K. If the top and side surfaces also have an emissivity of 0.80 and are maintained at 900 K, the net rate of radiation heat transfer from the top and side surfaces to the bottom surface is
(a) 194 kW

(b) 233 kW

(c) 288 kW

(d) 312 kW

(e) 242 kW