$\eta =\frac{\left| W \right|}{{{Q}_{H}}}=\frac{{{Q}_{H}}-\left| {{Q}_{L}} \right|}{{{Q}_{H}}}=\frac{2000-1200}{2000}=\frac{2}{5}$ کارنو: $Carnot$ $\eta \le {{\eta }_{\text{Carnot}}}\Rightarrow \eta \le 1-\frac{{{T}_{L}}}{{{T}_{H}}}\Rightarrow \frac{2}{5}\le \frac{{{T}_{H}}-{{T}_{L}}}{{{T}_{H}}}\Rightarrow \frac{2}{5}\le \frac{400}{{{T}_{H}}}\Rightarrow {{T}_{H}}\le 1000K$ ${{T}_{H}}-{{T}_{L}}=400\Rightarrow {{T}_{L}}\le 600K\Rightarrow {{\theta }_{L}}\le 600-273\Rightarrow {{\theta }_{L}}\le 327{}^\circ C$