To find the area of a circle, we can use the formula:
\[ A = \pi r^2 \]
where \( r \) is the radius of the circle. The radius is half of the diameter, so if the diameter is 21 mi, then the radius \( r \) is:
\[ r = \frac{21}{2} = 10.5 , \text{mi} \]
Now, plug the radius into the area formula:
\[ A = \pi r^2 = 3.14 \times (10.5)^2 \]
Calculating \( (10.5)^2 \):
\[ 10.5^2 = 110.25 \]
Now substitute back into the area formula:
\[ A = 3.14 \times 110.25 \]
Calculating this:
\[ A = 346.19 , \text{mi}^2 \]
Thus, the area of the circle is 346.19 mi² when rounded to the nearest hundredths place.
So the correct answers to your questions are:
- 346.19 mi²
- A = πr² (This is the formula for finding the area of a circle.)