Four charges are situated as shown in the diagram (each grid line is separated by 1 meter). The two upper charges have a charge of -3 C (-310-6 C). The two lower charges have a charge of +3 C (+310-6 C). 13) What is the magnitude of the net electric field at the point (0, 0)? 14) What is the net electric potential at the point (0, 0)? +y +x 15) What is the magnitude of the net force on the upper right charge? 16) What is the net work needed to bring in all four charges from infinity to build this configuration?