Chapter 4 - Writing Linear Functions - 4.2 - Writing Equations in Point-Slope Form - Exercises - Page 185: 19

$y=-9$

Let $(x_{1},y_{1})=(1,-9)$ and $(x_{2},y_{2})=(-3,-9)$ The slope of the line is $m=\frac{y_{2}-y_{1}}{x_{2}-x_{1}}=\frac{-9-(-9)}{-3-1}=\frac{0}{-4}=0$ We can write the equation of a line using the value of slope $m=0$ and the point $(1,-9)$. $y-y_{1}=m(x-x_{1})$ $\implies y-(-9)=0(x-1)$ $\implies y+9=0$ $\implies y=-9$