The area of a circle is calculated as follows:
[tex]A=\pi\cdot\frac{D^2}{4}[/tex]where D is the diameter of the circle.
Substituting with D = 64 mi, we get:
[tex]\begin{gathered} A=3.14\cdot\frac{64^2}{4} \\ A=3.14\cdot\frac{4096^{}}{4} \\ A=3.14\cdot1024 \\ A=3215.36\text{ mi}^2 \end{gathered}[/tex]