Two sinusoidal waves, identical except for phase, travel in the same direction along a string, producing a net wave

y $($x$,$ t$)=(4\mathrm{.}00$ mm$)$ sin$(13\mathrm{.}0$x $-6\mathrm{.}30$t $+0\mathrm{.}880$ rad$),$

with x in meters and t in seconds. What are $($a$)$ the wavelength $1$ of the two waves, $($b$)$ the phase difference between them, and $($c$)$ their amplitude ym$?$