.==> \(\frac{H}{{H'}} = \frac{{(T_1^4 - T_0^4)}}{{(T_2^4 - T_0^4)}} = \)\(\frac{{{{400}^4} - {{200}^4}}}{{{{600}^4} - {{200}^4}}}\)
or \(H' = \frac{{(16 + 4)(16 - 4)H}}{{(36 + 4)(36 - 4)}}\)\( = \frac{3}{{16}}H\)
[Assume steady state heat conduction]