How can I show that the bulk modulus is about r^-4?

[joemmonster]

Homework Statement

Using the equations, show the bulk modulus is about r^-4.

Homework Equations

The Attempt at a Solution

Tried to plug Uij but it is not same as U. To be honest, I don't know where to start.

 

[Mapes]

What values were you given for $m$ and $n$? If you weren't given values, what pair potential have you discussed in class?

What's the relationship between $r$ and $\Omega$?