Equations of horizontal and vertical lines only have one variable. The equation x = 4 represents a vertical line which crosses the x-axis at the point (4, 0). Every ordered pair with 4 as its first coordinate is a solution. (The equation means “x is equal to 4, and y can be whatever it wants.”)
Similarly, the equation
y = –3
is a horizontal line which crosses the y-axis at (0, –3).
The point where the horizontal and vertical lines intersect is also easy to find.