The rate of cooling at 600 K, if surrounding temperature is 300 K is H. The rate of cooling at 900 K is
163H
2H
3H
23H
By Stefan's law, Rate of cooling, H directly proportional to (T4-T04)
H'H= (900)4-(300)4(600)4-(300)4 = 94-3464-34 = 34(34-1)34(24-1)
H' = 163H