$8.$ A wave is modeled with the function y$($x$,$ t$)=(0\mathrm{.}25$m$)$ cos $(0\mathrm{.}30$ m$)$x $-(0\mathrm{.}90$ m$)$ t$).$Find the $($a$)$ amplitude, $($b$)$ wave number, $($c$)$ angular frequency, $($d$)$ wave speed, $($e$)$ wavelength, and $($f$)$ period of the wave.