Answer
(a) does not exist.
(b) $x=-7$
Work Step by Step
(a) A line perpendicular to $y=8$ will have an undefined slope. The line will have an equation in the form of $x=a$. With point $(-7,4)$, we have $x=-7$ which means the slope-intercept form $y=mx+b$ does not exist.
(b) Form standard form, we have $x=-7$
