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In the figure the four particles form a square of edge length a = 6.20 cm and have charges q1 = 8.52 nC, q2 = -20.2 nC, q3 = 20.2 nC, and 94=-8.52 nC. What is the magnitude of the net electric field produced by the particles at the square's center? 91 92 43 Number i Units