Answer
$a.$
A line parallel to the given line has slope $m=0$
$b.$
A line perpendicular to the given line has undefined slope.
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).
Any two horizontal lines are parallel.
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$ y=9\qquad$ is a horizontal line, with slope m=0..
(passes through all points whose y-coordinate is 9).
A line perpendicular to it is vertical, with undefined slope.
$a.$
A line parallel to the given line has slope $m=0$
$b.$
A line perpendicular to the given line has undefined slope.
