To find the area of a circle, you can use the formula:
\[ \text{Area} = \pi r^2 \]
where \( r \) is the radius. The radius is half of the diameter. If the diameter is 21 miles, then:
\[ r = \frac{21}{2} = 10.5 \text{ miles} \]
Now, substitute the radius 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, substitute this value back into the area formula:
\[ \text{Area} = 3.14 \times 110.25 \]
Calculating this gives:
\[ \text{Area} \approx 346.19 \text{ square miles} \]
Hence, rounding to the nearest hundredths place, the area of the circle is:
346.19 mi² (or 346.19 square miles).
So the correct response is: 346.19 mi squared.