b
Rate of heat radiated at $(227+273)\,K$
$=7\,cals/(cm^2s)$
Let rate of heat radiated at $(727+273)\,K=x\,cals/(cm^2s)$
By $Stefan's\,law,\,7\propto(500)^4\,and\,x\propto(1000)^4$
$\therefore \frac{x}{7} = {2^4} \Rightarrow x = 7 \times {2^4} = 112\,cals/\left( {c{m^2}s} \right).$