Two tiny spheres with charges +20×10^-8 C and -5.0×10^-8 C with 10cm apart. Point P in the middle of it. a) Calculate the electric field E at point P.
b) Find where in the region the electric field would be zero.
c) Calculate the force on a -4.0 x 10^-8 C charge placed at P.​

I think it's c but Iam not sure

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.