In $\triangle ABC$, points $X$ and $Z$ are on $\overline{AB}$ and $Y$ is on $\overline{AC}$ such that $\overline{XY}\parallel \overline{BC}$ and $\overline{ZY}\

\(In $\triangle ABC$, points $X$ and $Z$ are on $\overline{AB}$ and $Y$ is on $\overline{AC}$ such that $\overline{XY}\parallel \overline{BC}$ and $\overline{ZY}\parallel \overline{XC}$. If $AZ = 8$ and $ZX = 4$, then what is $XB$?\)