Answer
$0.28$
Work Step by Step
As we know that
Total heat input= Work done+Heat exhausted
Total heat input= 340+870=1210 J
Now we can find the efficiency as follows:
$\eta=\frac{Work \space done}{Heat \space input}$
We plug in the known values to obtain:
$\eta=\frac{340}{1210}=0.28$