Two equal positive charges of magnitude +q separated by a distance d are surrounded by a uniformly charged thin spherical shell of radius 2d bearing a total cha

Two equal positive charges of magnitude +q separated by a distance d are surrounded by a uniformly charged thin spherical shell of radius 2d bearing a total charge -24 and centred at the midpoint between the two positive charges. The net electric field at distance r from the midpoint (>> d) is (a) zero (b) proportional to d (c) proportional to 1/r3 (d) proportional to 1/*