4. Charges of 3.5 /C are placed at each of four corners of a square 12 cm on a side. All are positive except the charge on the lower left corner which is negative. a) (5 points) What is the magnitude and direction of the electric force on the negative charge at the lower left corner of the square? b) (5points) If the lower left charge from part a) was the last to be added to assemble the charge array, what was the voltage at that point prior to adding this last charge? c) (5 points) What is the magnitude and direction of the electric field at the location of this same negative charge