 A=pi*a^2=pi(y/25)^2=pi*y^2/625
 Rr=31171.2*(A/y^2)^2
 and finally, Rr=(31171.2*pi^2)/(625^2)
 The radiation resistance for single turn = 0.787577 ohm
 The radiation resistance for turn loop = 64.581345 ohm
 The answer is wronge in the given textbook