Chapter 2 - Functions, Equations, and Graphs - 2-4 More About Linear Equations - Practice and Problem-Solving Exercises - Page 86: 13

$y+2=0$

Recall: The equation of a line whose slope is $m$ and passes through the point $(x_1, y_1)$ is: $$y-y_1=m(x-x_1)$$ Thus, the equation of the line whose slope is $0$ and passes through the point $(4, -2)$ is: \begin{align*} y-(-2)&=0(x-4)\\ y+2&=0 \end{align*}