Answer:
B
Step-by-step explanation:
Use the Heron's formula for the area of the triangle:
[tex]A=\sqrt{p(p-a)(p-b)(p-c)},[/tex]
where a, b, c are lengths of triangle's sides and [tex]p=\dfrac{a+b+c}{2}.[/tex]
Since [tex]a=11.5,\ b=13.7,\ c=12.2,[/tex] then
[tex]p=\dfrac{11.5+13.7+12.2}{2}=18.7.[/tex]
Hence,
[tex]A=\sqrt{18.7(18.7-11.5)(18.7-13.7)(18.7-12.2)}=\sqrt{18.7\cdot 7.2\cdot 5\cdot 6.5}=\\ \\=\sqrt{11\cdot 1.7\cdot 9\cdot 4\cdot 0.2\cdot 5\cdot 5\cdot 1.3}=30\sqrt{11\cdot 1.7\cdot 0.2\cdot 1.3}=30\sqrt{4.862}\approx 66.1\ un^2.[/tex]
