To find the area of a circle given the diameter, you can use the formula:
\[ \text{Area} = \pi r^2 \]
where \( r \) is the radius of the circle. The radius is half of the diameter. Given that the diameter is 21 mi, the radius will be:
\[ r = \frac{21}{2} = 10.5 \text{ mi} \]
Now, substituting \( r \) into the area formula using \( \pi \approx 3.14 \):
\[ \text{Area} = 3.14 \times (10.5)^2 \]
First, calculate \( (10.5)^2 \):
\[ (10.5)^2 = 110.25 \]
Now calculate the area:
\[ \text{Area} = 3.14 \times 110.25 \approx 346.19 \text{ mi}^2 \]
Therefore, the area of the circle is approximately 346.19 mi².
So, the correct response is:
346.19 mi squared.