Answer
$498$ square centimeters.
Work Step by Step
Using that we have obtained the lengths of the sides: $s=0.5(a+b+c)=0.5(42+26.5+38.3)=53.4$
Then the area of the triangle is: $\sqrt{s(s-a)(s-b)(s-c)}=\sqrt{53.4(53.4-42)(53.4-26.5)(53.4-38.3)}\approx498$ square centimeters.