S.65 7-2

\eta_{\max}=\frac{T_1-T_2}{T_1}=1-\frac{T_2}{T_1}=1-\frac{\left(25°C+273{,}15\right)K}{\left(540°C+273{,}15\right)K}=0{,}633...\approx0{,}63=63\%