## Precalculus (10th Edition)

$9.56$ square units
By Heron's theorem $K=\sqrt{s(s-a)(s-b)(s-c)}$, where $s=\frac{a+b+c}{2}.$ Hence, $s=\frac{9+6+4}{2}=9.5$. Thus, $K=\sqrt{9.5(9.5-9)(9.5-6)(9.5-4)}\approx9.56.$