Answer
$y=-1$
Work Step by Step
Use the slope formula $m=\frac{y^2-y^1}{x^2-x^1}$ and the point-slope form $y-y_1=m(x-x_1)$ to solve this problem.
Passing through $(-3,-1)$ and $(4,-1)$
$\frac{-1+1}{4+3}=0$
$y+1=0(x+3)$
$y+1=0$
$y=-1$