Current Attempt in Progress

If $y(x,t)=(5\mathrm{.}2mm)sin[kx+(780ra\frac{d}{s})t+]$ describes a wave traveling along a string, how much time does any given point on the strin take to move between displacements $y=+3\mathrm{.}6mm$ and $y=-3\mathrm{.}6mm?$