To calculate the diameter (d) of the circle using the formula \( d = \frac{C}{\pi} \), with a circumference \( C \) of 125.6 feet and using \( \pi \approx 3.14 \), we can substitute the values into the formula:
\[ d = \frac{125.6}{3.14} \]
Now, performing the division:
\[ d \approx \frac{125.6}{3.14} \approx 40.06 \text{ feet} \]
Thus, the diameter \( d \) is approximately 40.06 feet.