#### Answer

$m=0$

#### Work Step by Step

$\bf{\text{Solution Outline:}}$
To find the slope and the graph of the given equation, $
y=-4
,$ use the slope and graph of lines in the form $y=b.$
$\bf{\text{Solution Details:}}$
Since lines of the form $y=b$ (where $b$ is a constant) have a slope of $0,$ then the slope of the line defined by the given equation is
\begin{array}{l}\require{cancel}
m=0
.\end{array}
The graph of lines in the form $y=b$ is a horizontal line that passes through the $y$-axis at $b.$