#### Answer

$y=12$

#### Work Step by Step

RECALL:
(1) The slope-intercept form of a line's equation is $y=mx+b$ where $m$=slope and $(0, b)$ is the line's y-intercept.
(2) A line with a slope of zero is horizontal, the equation of which is of the form $y=k$ where $k$ is the y-intercept. All points on the line have a y-coordinate of $k$.
The given line has a slope of zero therefore it is horizontal and its equation is of the form $y=k$.
The line contains the point $(-3, 12)$.
The y-coordinate of this point is $12$.
Thus, the line's equation is $y=12$.
The equation of the line cannot be written in slope-intercept form.