c
\({\text{E}} = \sigma \,{\text{A}}\,{{\text{T}}^{\text{4}}}\,\,\, \Rightarrow \,\,\,\frac{{{E_1}}}{{{E_2}}} = {\left( {\frac{{{r_1}}}{{{r_2}}}} \right)^2} \times {\left( {\frac{{{T_1}}}{{{T_2}}}} \right)^4}\)
\(\frac{{{E_1}}}{{{E_2}}} = {\left( {\frac{8}{2}} \right)^2} \times {\left( {\frac{{400}}{{800}}} \right)^4} = 1:1\)