Answer:CStep-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=2,\ b=7,\ c=8,[/tex] then[tex]p=\dfrac{2+7+8}{2}=8.5.[/tex]Hence,[tex]A=\sqrt{8.5(8.5-2)(8.5-7)(8.5-8)}=\sqrt{8.5\cdot 6.5\cdot 1.5\cdot 0.5}=\\ \\=\sqrt{41.4375}\approx 6.4\ un^2.[/tex]