At a distance of 1.88 m from a point charge of +2.42 C, there is an equipotneial surface. At greater distances there are additional equipotential surfaces. The potential difference between any two successive surfaces is 1.15 x 103 V. Starting at a distance of 1.88 m and moving radially outward, how many of the additional equipotential surfaces are crossed by the time the electric field has shrunk to one-half of its initial value? Do not include the starting surface.