[mahmoud khodary]

E=P/(4*pi *r^2)
P=100 r=6m Pi=3.14(constant)
so E=100/(4*3.14*6^2) =0.22
AND FOREBYE

r^2=P/(E*4*Pi)
r^2=60/(0.22*4*3.14) = 21.7
r= 4.66m