Using the formula for area of a circle: area = pi x r^2
You now have:
225pi ft^2 = pi x r^2
Divide both sides by pi:
225 = r^2
Take the square root of both sides:
r = 15
The radius is 15 feet.
The diameter is the radius x 2:
Diameter = 15 x 2 = 30 feet.
Answer: 30 feet.