Answer
$12\sqrt 5$
Work Step by Step
In order to use Heron's Formula we have to find the semiperimeter:
$s=\frac{1}{2}(a+b+c)$
$s=\frac{1}{2}(7+8+9)$
$s=\frac{1}{2}*24$
$s=12$
We can use Heron's Formula from here:
$A=\sqrt{s(s-a)(s-b)(s-c)}$
$A=\sqrt{12(12-7)(12-8)(12-9)}$
$A=\sqrt{12*5*4*3}$
$A=\sqrt{720}$
$A=12\sqrt 5$
$A\approx 26.83$
