A longitudinal wave in a stretched slinky $($spring$)$ given by x$($x$,$t$)=8\mathrm{.}0$mm$$cos$(3\mathrm{.}7$rad$/$cm$$x$+4\mathrm{.}0$rad$/$s$$t$)$x$($x$,$t$)=8\mathrm{.}0$mm$$cos$(3\mathrm{.}7$rad$/$cm$$x$+4\mathrm{.}0$rad$/$s$$t$).$ What is the wavelength of these waves?