The equation for the x-axis is y = 0.
Then, the equation of a line perpendicular to y = 0 is x = constant.
You can observe it in the figure below.
So, since the line passes throught the point P = (1, 3), the perpendicular has to pass thorught x = 1.
Then, since the line is x = constante, the line is x =1.
Answer: x = 1.
