Answer
$442,815.6$ square miles
Work Step by Step
By Heron's formula, $K=\sqrt{s(s-a)(s-b)(s-c)}$, where $s=\frac{a+b+c}{2}.$
Hence, here we have
$s=\frac{1028+1046+965}{2}=1519.5$,
Thus,
$K=\sqrt{1519.5(1519.5-1028)(1519.5-1046)(1519.5-965)}\approx442,815.6$ square miles