solution
for this case we can use the Herons formula given by:
[tex]A=\sqrt[]{s(s-a)(s-b)(s-c)}[/tex]
Where s is the semiperimeter given by:
[tex]s=\frac{a+b+c}{2}=\frac{33.4+28.5+22.3}{2}=42.1[/tex]
And we can find the area on this way:
[tex]A=\sqrt[]{42.1(42.1-33.4)(42.1-28.5)(42.1-22.3)}=314.05[/tex]
And rounded to the nearest tenth would be:
314.1
