Two small insulating spheres with radius 4.50×10−2 mare separated by a large center-to-center distance of 0.510 m . One sphere is negatively charged, with net charge -2.20 μC , and the other sphere is positively charged, with net charge 3.95 μC . The charge is uniformly distributed within the volume of each sphere.

What is the magnitude E of the electric field midway between the spheres?

Take the permittivity of free space to be ϵ0 = 8.85×10−12 C2/(N⋅m2) .