Answer
(a) $260J$
(b) $0.3768$
Work Step by Step
(a) We know that
$Heat\space provided=Work \space done +Heat \space exhausted$
$\implies Work \space done =Heat \space provided -Heat \space exhausted$
We plug in the know values to obtain:
$Work \space done=690-430=260J$
(b) The efficiency of the engine can be determined as
$\eta=\frac{Work\space done}{Heat \space input }$
We plug in the known values to obtain:
$\eta=\frac{260}{690}$
$\eta=0.3768$
