Answer
$ \eta = 33.33\%$
Work Step by Step
We know that
$ W=Q_1 -Q_2$
$200J = Q_1 -400J$
$ Q_1 = 600J$
Also
$ \eta = \frac{W}{Q_1}$
$\eta = \frac{200J}{600J}$
$ \eta = 33.33\%$
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