The efficiency of a Carnot engine is given by
[tex]\eta=1-\frac{T_C}{T_H}[/tex]Where TC is the temperature of the cold source in kelvin and TH is the temperature of the hot source in kelvin.
Let us first convert the given temperatures from celsius to kelvin.
[tex]\begin{gathered} T_C=-20+273=253K \\ T_H=1500+273=1773K \end{gathered}[/tex]So, the efficiency is
[tex]\begin{gathered} \eta=1-\frac{253}{1773} \\ \eta=0.857 \\ \eta=85.7\% \end{gathered}[/tex]Rounding off to a whole number
[tex]\eta=86\%[/tex]Therefore, the efficiency of the engine is 86%
