A sinusoidal wave on a string is described by the equation y $=(0\mathrm{.}107$ m$)$ sin $(0\mathrm{.}775$ x $-42\mathrm{.}9$ t$),$ where x and y are in meters and t is in seconds. If the linear mass density of the string is $10\mathrm{.}7$ g$/$m $...$

a$)...$ determine the phase constant.