When we have an equation of the form x = c, with c a constant number, then the graph of the line is a vertical line, parallel to the y-axis.
When we have an equation of the form y = k, with k a constant number, then the graph of the line is a horizontal line, parallel to the x-axis.
In this case, we have:
y = 5:
Is a line parallel to the x-axis.
x = 6:
Is a line parallel to the y-axis.
Since the two axes are perpendicular to each other, the lines must be perpendicular to each other.
Thus, the correct answer is perpendicular.