The given figure is a trapezium as two sides are parallel and two are non parallel.
The parallel sides of the trapezium are a=3 mi and b=11 mi.
The height of the trapezium is h=8.7 mi.
The expression for the area of the trapezium is,
[tex]\text{Area}=\frac{1}{2}(a+b)\times h[/tex]
Substituting the known values in the above expression,
[tex]\begin{gathered} \text{Area}=\frac{1}{2}(3\text{ mi+11 mil)}\times8.7\text{ mi} \\ =\frac{14\text{ mi}}{2}\times8.7\text{ mi} \\ =7\text{ mi}\times8.7\text{ mi} \\ =60.9mi^2 \end{gathered}[/tex]
Thus, the required area is 60.9 square miles.
