Question

How do you find the slope perpendicular to `x=-7`?

Answer 1

`0`

Explanation:

`x=-7` is a straight line parallel to the y-axis cutting the x-axis at -7. Its slope is undefined.

So a line perpendicular to this line will be a horizontal line parallel to the x-axis and cutting the y-axis at any point c.
Such a line will have zero gradient.