Finding force from potential energy U(x) = αx⁴ at x = -0.660 m

[javacola]

Homework Statement

A force parallel to the x-axis acts on a particle moving along the x-axis. This force produces a potential energy U(x) given by U(x)= alpha x^4 where alpha=1.50 J/m^4.

What is the force when the particle is at position x = -0.660 m?

Homework Equations

The Attempt at a Solution

I know this has to do with derivaties, a the answer will comes from 4*1.5*some other number cubed. I just don't know what.

 

[rock.freak667]

How does force relate to the potential U? (This will tell you what to cube)