==> \(\frac{{{K_S}A({\theta _1} - {\theta _2})}}{{2x}} = \frac{{2KA({\theta _1} - \theta )}}{x}\)
\(\because {K_S} = \frac{{2 \times 2K \times K}}{{(2K + K)}} = \frac{4}{3}K\) and \(({\theta _1} - {\theta _2}) = 36^\circ \)
==> \(\frac{{\frac{4}{3}KA \times 36}}{{2x}} = \frac{{2KA({\theta _1} - \theta )}}{x}\)
Hence temperature difference across wall \(A\) is \(({\theta _1} - \theta ) = {12^o}C\)