$-1$ If a wave $y(x,t)=(6\mathrm{.}0mm)sin(kx+(600ra\frac{d}{s})t+)$ travels along a string, how much time does any given point on the string take to move between displacements $y=+2\mathrm{.}0mm$ and $y=-2\mathrm{.}0$ mm $?$