To find the diameter \( d \) of a circle given the circumference \( C \), you can use the formula:
\[ d = \frac{C}{\pi} \]
Given that \( C = 21.98 \) ft and using \( \pi \approx 3.14 \):
\[ d = \frac{21.98}{3.14} \]
Now, let's perform the division:
\[ d \approx \frac{21.98}{3.14} \approx 7.00 \text{ ft} \]
Thus, the diameter \( d \) of the circle is approximately 7.00 feet.