Question 757962
area is directly proportional to
the square of its radius.
A = kr^2
(k is the constant of proportionality)
12.566 = k 2^2
   k = 12.566/4
   k = 3.1415
Formula: A = 3.1415 r^2
       78.54 = 3.1415 r^2
       78.54/3.1415 = r^2
               r^2 = 25
                 r = 5cm

Hope this helps.
:-)