Write the equation of line perpendicular to y = 4 that passes through (5, 2).

x=5

Explanation;
y=4 is a horizontal line, and we know this because all we have is the y intercept; 4 (the y-intercept is the point on the line that intercepts the y axis) There is also no x value. This is the equation for a horizontal line:

y=b
B is the y-intercept.

A line perpendicular to a horizontal line would be a vertical line. This is the equation for a vertical line:

x=d
D is the x-intercept (the point on the line that intercepts the x axis)

So to answer the question, we just need to plug the x value of the point (5,2) into x=d.

(5,2)-> 5 is the x coordinate

Therefore, x=5

I hope this helps! Please comment if you have any questions.