The line that is perpedicular to the y-axis is:
y = -6
Which equation represents a line which is perpendicular to the y-axis?
The y-axis can be defined by the equation:
x = 0.
Any equation of the form:
x = a
Is perpendicular to any equation of the form:
y = b
x = a is a vertical line, y = b is an horizontal line.
From the options, the only one of the form y = b is the third option:
y = -6
That line is perpendicular to the y-axis.