In this problem we have to use the Hero formula so first we have to find s:
[tex]s=\frac{a+b+c}{2}[/tex]
and then we replace the sides of the triangle:
[tex]s=\frac{12+11+7}{2}=\frac{30}{2}=15[/tex]
and with s we can use the formula of A so:
[tex]A=\sqrt[]{s(s-a)(s-b)(s-c)}[/tex]
and replace the data so:
[tex]A=\sqrt[]{15(15-12)(15-11)(15-7)}[/tex]
and we simplify it so:
[tex]\begin{gathered} A=\sqrt[]{15(3)(4)(8)} \\ A=\sqrt[]{1440} \\ A\approx37.95 \end{gathered}[/tex]
