Answer: The slope of a line that is parallel to it = zero.
There is no slope of a line perpendicular to it.
Explanation:
For the graph y=12 ,
Since slope of line
[as there is no change in y coordinate]
Hence, the slope of line y=12 is zero
, thus every line parallel to y=12 has same slope , i.e. zero
Let the slope of line parallel to it be
, then

Thus, there is no slope of line perpendicular to y=12 .