3730 N/C
The intensity of the electric field follows the inverse square law. Since everything except the distance is remaining constant, then the force will vary with the inverse square of the ratio of the change. So first, lets calculate the ratio of the change in distance.
22.3 / 7.8 = 2.858974359
And since we actually want the square of the distance...
2.858974359^2 = 8.173734385
And since the distance increased, that means the force will decrease. So we get
30500 / 8.173734385 = 3731.464538
Rounding to 3 significant figures gives 3730 N/C.
