Answer
$6.9$ square feet.
Work Step by Step
Using that we have obtained the lengths of the sides: $s=0.5(a+b+c)=0.5(3.2+4.3+5.4)=6.45$
Then the area of the triangle is: $\sqrt{s(s-a)(s-b)(s-c)}=\sqrt{6.45(6.45-5.4)(6.45-4.3)(6.45-3.2)}\approx6.9$ square feet.