Answer
(a) $2600 J$
(b) $\epsilon = 28.9 \%$
Work Step by Step
(a) Work output,
$W = |Q_H| - |Q_C|$
$W = 9000 J - 6400 J $
$W = 2600 J$
(b) Thermal efficiency,
$\epsilon = \frac{W}{|Q_H|} \times 100 $
$\epsilon = \frac{ 2600 J}{9000 J } \times 100 $
$\epsilon = 28.9 \%$
