A spherical conductor with a 0.413 m radius is initially uncharged. How many electrons should be removed from the sphere in order for it to have an electrical potential of 7.50 kV at the surface

Ahuge (essentially infinite) horizontal nonconducting sheet 10.0 cm thick has charge uniformly spread over both faces. the upper face carries +95.0 nc/m2 while the lower face carries -25.0 nc/ m2. what is the magnitude of the electric field at a point within the sheet 2.00 cm below the upper face? (ε0 = 8.85 × 10-12 c2/n · m2)