Depending on what "a circle of 480 feet" means, the radius will
have different values.
If the radius is 480 feet, then that is your answer.
If the diameter is 480 feet, then its radius is 480/2 = 240
feet.
If the circumference is 480 feet, then its radius is 480/2(pi) =
240/(pi) = 76.39 feet.