Решение.
\[ \begin{align}
& \eta =\frac{A}{{{Q}_{1}}}\ \ \ (1),\ \eta =1-\frac{{{T}_{2}}}{{{T}_{1}}}\ \ \ (2),\ \frac{A}{{{Q}_{1}}}=1-\frac{{{T}_{2}}}{{{T}_{1}}},\ A={{Q}_{1}}\cdot (1-\frac{{{T}_{2}}}{{{T}_{1}}}), \\
& \ {{T}_{1}}\ =3\cdot {{T}_{2}},\ A={{Q}_{1}}\cdot (1-\frac{{{T}_{2}}}{3\cdot {{T}_{2}}}),\ A={{Q}_{1}}\cdot (1-\frac{1}{3}),\ A={{Q}_{1}}\cdot \frac{2}{3}\ \ \ (3). \\
\end{align} \]
А = 28 кДж.