Four particles are located at the corners of a square that is \(50 \mathrm{~mm}\) on a side. All four particles carry a charge of magnitude \(3.0 \mathrm{nC}\), with positive charge at the lower left corner and negative charge at the other corners. Draw the electric field vectors at the center of the square caused by each of the four source charges, then determine the magnitude and direction of the electric field at the center of the square.