To calculate the radius \( r \) of a circle (tree trunk) from its circumference \( C \), we can use the formula for circumference:
\[ C = 2\pi r \]
Given that the circumference \( C \) is 157 inches, we can rearrange the formula to solve for the radius \( r \):
\[ r = \frac{C}{2\pi} \]
Now, substituting \( C = 157 \) inches and \( \pi \approx 3.14 \):
\[ r = \frac{157}{2 \times 3.14} \]
Calculating the denominator:
\[ 2 \times 3.14 = 6.28 \]
Now we can calculate \( r \):
\[ r = \frac{157}{6.28} \approx 25.00 \text{ inches} \]
So, the radius \( r \) of the tree trunk is approximately 25 inches.