Answer
Please see the work below.
Work Step by Step
We know that
$Q=mc\Delta T+mL_v$
We plug in the known values to obtain:
$Q=(420)(4184)(100-20)+(420)(2257000)$
$Q=1.0885\times 10^{12}J$
Now we can find the duration as
$t=\frac{Q}{P}$
We plug in the known values to obtain:
$t=\frac{1.0885\times 10^{12}}{200\times 10^6}$
$t=5400s \approx 1.5 h$
