at r = 2R> R The expression for the electric field will be given by: (2R)^2*E=kQ. Where, k=(9*10^9)N.m/C^2, Q=(8*10^-10)C and R=0.025m. So substituting and clearing, we have that the magnitude of the electric field will be: E=(9*10^9)*(8*10^-10)/((2*0.025)^2)=2880 N / C.