Answer
$7517.38$ square feet
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
$s=\frac{87+190+173}{2}=225$,
Thus,
$K=\sqrt{225(225-87)(225-190)(225-173)}\approx7,517.38$ square feet