Answer
$y=-7$
Work Step by Step
Using $y-y_1=m(x-x_1)$ or the Point-Slope Form, the equation of the line with the given point $(
3,-7
)$ and slope $m=
0
$ is
\begin{array}{l}\require{cancel}
y-(-7)=0(x-3)
\\\\
y+7=0
\\\\
y=-7
.\end{array}