Given the lines
$$r \equiv \frac { x - 2 } { 1 } = \frac { y + 1 } { 1 } = \frac { z + 4 } { - 3 } , \quad s \equiv \left\{ \begin{array} { l } x + z = 2 \\ - 2 x + y - 2 z = 1 \end{array} . \right.$$
a) (1.5 points) Write an equation of the common perpendicular line to $r$ and $s$.
b) (1 point) Calculate the distance between $r$ and $s$.