Answer
$a.$
A line parallel to the given line has undefined slope.
$b.$
A line perpendicular to the given line has slope $m=0$
Work Step by Step
If two nonvertical lines are parallel, then they have the same slope.
If two nonvertical lines are perpendicular, then the product of their slopes is -1.
Any two vertical lines (with undefined slope) are parallel.
A vertical line (slope undefined) is perpendicular to any horizontal line (with slope m=0)
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$ x=6\qquad$ is a vertical line.
(passes through all points whose x-coordinate is 4)
$a.$
A line parallel to the given line has undefined slope.
$b.$
A line perpendicular to the given line has slope $m=0$
