Answer
(a) $1.16GW$
(b) $1.71GW$
Work Step by Step
(a) We know that
$\eta=\frac{Work\space done}{Heat \space input}$
We plug in the known values to obtain:
$0.32=\frac{838}{Heat\space input}$
$\implies Heat\space input=2618.75MW$
Now $Heat \space provided=Work\space done+Heat\space discarded$
$\implies Heat\space discarded=Heat \space provided-Work\space done$
We plug in the known values to obtain:
$Heat \space discarded=2618.75-838=1780.75MW=1.16GW$
(b) As $\eta=\frac{Work\space done}{Heat\space input}$
We plug in the known values to obtain:
$0.32=\frac{838}{Heat\space input}$
$\implies Heat\space input=2618.75MW=1.71GW$