Hint for the first part. See

here. Specifically look at option 3 under the "Mathematical Description" heading. In 1-D terms this means we are looking for a function $\displaystyle \Phi$ that satisfies

$\displaystyle F = -\frac{d \Phi}{dx}$

Can you find such a function?

For the second part, an equilibruim point is where the force is 0 N. You will find one of those. To tell if it will be a stable or unstable point, imagine a small displacement from equiilibrium. Does the graph of F tell you if the object is going to move back to the equilibrium point, or move away from it?

-Dan