Answer
$30 \ square \ units $
Work Step by Step
According to Heron's theorem, the area of a triangle with sides $a,b$ and $c$ is given by:
$K=\sqrt{s(s-a)(s-b)(s-c)}$
where $s=\dfrac{a+b+c}{2}$
We have: $a=6, b=5, c=8$
So, $s=\dfrac{12+13+5}{2}=15$
In order to find the area of a triangle we will have to substitute the data into Heron's theorem.
$K=\sqrt{15(15-12)(15-13)(15-5)}=30 \ square \ units $