Please help me with these questions with detailed explanation!

Problem: What is the potential at the center of a solid conducting sphere of radius 9e-09 cm that has a charge of 3e-09 C? 0 3.00e+11 V 0 3.33e+21 V OO V 0 3.00e+09 V 0 3.33e+01 V Problem: A very thin spherical plastic shell of radius 15 cm carries a uniformly distributed charge of 9.3 nC on its outer surface. An uncharged solid metal block is placed nearby. The block is 10 cm thick, and it is separated by 10.9 cm from the surface of the sphere. 15 cm z The magnitude of the electric field at the center of the metal block due only to the charges on the block itself is: 0 8.770+02 N/C 0 3.310+03 N/C 0 2.71e+02 N/C 0 8,770-02 N/C 0 0.77e+11 N/C Problem: You stand at location A, a distance d from the origin, and hold a small charged ball. You find that the electric force on the ball is 0.005 N. You move to location B, a distance 2d from the origin, and find the electric force on the ball to be 0.005 N. What object located at the origin might be the source of the field? O A charged infinite plane O A point charge O A uniformly charged hollow sphere D A dipole O A long uniformly charged rod