Hi, here is a practice question. I'm not sure where the equation of motion comes in to play. Any help would be much appreciated. Thanks!

The equation of motion for a particle of mass 1 in a quartic oscillator V(x)=(1/4)x^4 is ẍ+x^3=0. Suppose that the maximum amplitude of the oscillator is x(max). Find an expression for the time T that it takes to go from x=0 to x=x(max) and show that this time is inversely proportional to x(max).