Change in gravitational potential energy of four particles in a square

[peaceandlove]

Homework Statement

Four particles, each of mass 60.0 g, form a square with an edge length of d = 0.700 m. If d is reduced to 0.100 m, what is the change in the gravitational potential energy of the four-particle system?

Homework Equations

U = -GMm/r

The Attempt at a Solution

I found the U of the system when d = 0.700 m and then I found the U when d = 0.100 m. Using those two values, I found what I believe to be the change in the U of the system. However, I keep getting the wrong answer.

U_1=-6.45898846e-12
U_2=-2.60012192e-11
(delta)U=1.95422308e-11

 

[peaceandlove]

Nevermind, I figured it out.