Four spheres are arranged as in the figure in the corners of a 2cm-side square. The second sphere has a charge of -10 nC, the rest a charge of +10 nC. Point C is the center of the square, A is at the middle point of the side.
(a) Find, in components, the electric field at point C.
(b) Find the electric potential at points A and C.
(c) How much work is required to move a tiny charge of 10nC from C to A.