The area of a circle is:
Area = PI x r^2 ( r is the radius which is half the diameter)
Using the information in the problem:
254.34 = 3.14 x r^2
Divide both sides by 3.14:
81 = r^2
Take the square root of both sides:
r = 9
The diameter = 2r = 2(9) = 18 cm