$($Streamlines$)$ A velocity field is given by $u=y-1$ and $v=y-2,$ where $u$ and $v$ are in $\frac{m}{s}$ and $x$ and $y$ are in meters.

$($a$)$ Write the equation for the streamline that passes through the point $(x,y)=(4,3).$

$($b$)$ Enter the number of the streamline that passes through the point $(x,y)=(4,3)$ in the figure below.

$($c$)$ Enter the number of the streakline that passes through the point $(x,y)=(4,3).$