A very crude model for the neutron consists of an inner core of positive charges surrounded by an outer core of negative charges. Suppose the positive charge has a magnitude of +e and is uniformly distributed over a sphere of radius 0.500 x 10^-15 m and that the negative charge has a magnitude of -e distributed over a concentric shell of inner radius 0.500 x 10^-15 m and outer radius of 1.00 x 10^-15 m. Find the magnitude of the electric field at r = 0.250 x 10^-15 m, r = 0.500 x 10^-15 m, r = 0.750 x 10^-15 m, and r = 1.00 x 10^-15 m.