Answer
$Area=108\sqrt {10}\approx341.53$
Work Step by Step
$s=\frac{a+b+c}{2}=\frac{33+36+21}{2}=\frac{90}{2}=45$
$Area=\sqrt {s(s-a)(s-b)(s-c)}=\sqrt {45(45-33)(45-36)(45-21)}=\sqrt {45(12)(9)(24)}=\sqrt {116640}=108\sqrt {10}\approx341.53$