Circumference (around).
If the diameter (distance across) the circle is 8.5 feet, then multiply that by pi (3.14) to get the circumference (distance around the outside)
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A circle with an 18-foot diameter has an area of: 254.5 square feet.
None. A 12 foot diameter is the length across a circle: it is a linear distance, not an area.
The circumference is 59.66 feet.