==>\({\eta _B} = \frac{{{T_2} - {T_3}}}{{{T_2}}} = \frac{{{W_B}}}{{{Q_2}}}\)
\(\therefore\) \(\frac{{{Q_1}}}{{{Q_2}}} = \frac{{{T_1}}}{{{T_2}}} \times \frac{{{T_2} - {T_3}}}{{{T_1} - {T_2}}} = \frac{{{T_1}}}{{{T_2}}}\)
\(\therefore\) \({W_A} = {W_B}\)
\(\therefore\) \({T_2} = \frac{{{T_1} + {T_3}}}{2} = \frac{{800 + 300}}{2} = 550K\)