The area of a circle can be found using:
pi x r^2 (where r is the radius)
If the area of the circle is 255pi, then:
pi x r^2 = 255pi
Now we need to make r the subject:
r^2 = 255 (cancel the pi on both sides)
r = square root of 255
r = 15.96871942
Answer: 15.96871942 feet
Hope the answer helps :)