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Four uniform spheres, with masses mA = 200 kg, mB = 100 kg, mC = 1900 kg, and mD = 250 kg, have (x, y) coordinates of (0, 50 cm), (0, 0), (-80 cm, 0), and (40 cm, 0), respectively. Sphere A is then removed. Calculate the gravitational potential energy of the remaining three-particle system

And I do not understand why I cannot get the correct answer. Potential energy equals...

= -G(m1m2)/r

Or in my case...

= -G(100*1900/80 + 100*250/40 + 1900*250/120)

= -4.6433E-7 J

Do I need to account for the loss of sphere A? Or is my error not accounting for the opposite direction of sphere C? Thanks for any advice.