Answer
Please see the work below.
Work Step by Step
We know that
$P_{net}=e\sigma A(T_2^4-T_1^4)$
We plug in the known values to obtain:
$P=(1)(5.7\times 10^{-8})(0.0325)((900)^4-(300)^4)$
$P=1200W$
Now we can find the fraction as
$\frac{1200}{1500}=0.80$
