Solve the following problem given below:
Problem: Four point charges sit at the corners of a square having each side parallel to the x or y axis side with a length of 33.0 cm. Starting at the top left corner and moving around the square clockwise, the electric charge on the objects is 64.2 µC, -51.2 µC, 81.4 µC, and 31.4 µC.
Part A: What is the magnitude and direction of the force on the object at the top left of the square?
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I known the correct answer for above problem but I need to know how to get that. Thanks in advance!