To calculate the radius \( r \) of a circle given the circumference \( C \), use the formula for circumference:
\[ C = 2\pi r \]
You can rearrange the formula to solve for \( r \):
\[ r = \frac{C}{2\pi} \]
Now, plug in the given circumference \( C = 81.64 \) feet and use \( \pi \approx 3.14 \):
\[ r = \frac{81.64}{2 \times 3.14} \]
Calculating \( 2 \times 3.14 \):
\[ 2 \times 3.14 = 6.28 \]
Now substitute this value back into the equation for \( r \):
\[ r = \frac{81.64}{6.28} \]
Next, perform the division:
\[ r \approx 13.00 \text{ feet} \]
Thus, the radius \( r \) is approximately \( 13.00 \) feet.