#### Answer

The lines are perpendicular to each other.
Refer to the image below for the graph.

#### Work Step by Step

RECALL:
(1) A vertical line has an undefined slope and an equation of the form $x=h$.
(2) A horizontal line has a slope of $0$ and an equation of the form $y=k$.
(3) A horizontal line and a vertical line are perpendicular to each other.
$y=-3$ is a horizontal line whose y-intercept is $-3$.
$x=-3$ is a vertical line whose x-intercept is $-3$.
(refer to the attached image in the answer part above for the graphs)
According to (3) in the recall part above, the two lines are perpendicular to each other.