Step 1: Use Heron's formula.
The sides of the triangle are
\[
a=4,\quad b=5,\quad c=7
\]
The semi-perimeter is
\[
s=\frac{a+b+c}{2}
\]
\[
s=\frac{4+5+7}{2}
\]
\[
s=\frac{16}{2}=8
\]
Step 2: Apply Heron's formula.
Area of triangle is
\[
\Delta=\sqrt{s(s-a)(s-b)(s-c)}
\]
Substituting the values,
\[
\Delta=\sqrt{8(8-4)(8-5)(8-7)}
\]
\[
\Delta=\sqrt{8\cdot 4\cdot 3\cdot 1}
\]
\[
\Delta=\sqrt{96}
\]
\[
\Delta=\sqrt{16\cdot 6}
\]
\[
\Delta=4\sqrt{6}
\]
Step 3: Final conclusion.
Therefore, the area of the triangular plot is
\[
\boxed{4\sqrt{6}}
\]