Answer
See explanation.
Work Step by Step
(a) Thermal efficiency,
$\epsilon = \frac{W}{|Q_H|} $
$|Q_H| = \frac{W}{\epsilon} $
$|Q_H| = \frac{2.5 × 10^4 J}{0.66} $
$|Q_H| = 3.79 \times 10^4J$
(b) $Q_C = W - Q_H$
$Q_C = 2.5 × 10^4 J - 3.79 \times 10^4J$
$Q_C = -1.29 \times 10^4 J$
The temperature of heat source,
$\frac{Q_C}{Q_H} = \frac{T_C}{T_H}$
$T_H= (T_C)\frac{|Q_H|}{|Q_C|}$
$T_H= (20^oC + 273 K )\frac{3.79 \times 10^4J}{1.29 \times 10^4 J}$
$T_H= 861 K = 588^oC$
