Imagine a spring made of a material that is not very elastic, so that the spring force does not satisfy Hooke’s Law, but instead satisfies the equation F = −α x + β x3 , where α = 5.2 N/m and β = 700 N/m3 . Calculate the work done by the spring when it is stretched from its equilibrium position to 0.12 m past its equilibrium. Answer in units of mJ.