Four particles with charges of 8.9 μC, 3.9 μC, 1.6 μC and -11 μC are placed at the corners of a "4.2 m × 4.2 m" square. The acceleration of gravity is 9.81 m/s2 and the value of Coulomb constant is 8.98755 × 109 N m2/C2 . Determine the potential difference between the center of the square and infinity. Answer in units of V. Please show all steps, equations, and work.