A solid conducting sphere with a radius of 2 centimeters has a charge of 8 microcoulombs. Concentric with the solid sphere is a hollow conducting spherical shell with an inner radius of 4 centimeters, outer radius of 5 centimeters, and charge of -4 microcoulombs. Find the magnitude of the electric field in newtons per coulomb at a radius of 4.5 centimeters.