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.