Answer
Please see the work below.
Work Step by Step
We know that
$Rated \space output\space \times 1 year=840MW\times 1yr\times \frac{365days}{yr}\times \frac{24hr}{day}=7,358,400MWhr$
Now $capacity \space factor=\frac{Actual \space energy\space produced \space in\space year}{Energy \space it\space could \space in \space year}=\frac{6.8\times 10^9KW.h}{7,358,400MWh}=0.924$
