Find a line that is perpendicular from x=10 and one point, (4,5) The title is quite self-explainary ;)
I know that the answer is $y=5$, but I am not sure how does one person come to that conclusions showing all the steps. Can you please help me here?

I had to do my own version, using @Tharindu's knowledge for my assignment. Here it is if anyone wants a more detailed version. The coordinates are different, since I had a different question:
We need to find an equation that will create a line that is perpendicular to the equation $x=3.58$, given that one point on the line B. As shown in steps beforehand, the point $B$ is equal to $(14.99,8.28)$ 
Any equation in the form $x=c$ will always make a vertical line. A perpendicular line is a line that intersects on a right angle. Therefore, knowing that $x=3.58$ will always be a vertical line, the perpendicular line will a horizontal line. A horizontal line always has a $m$ value of 0. 
Therefore, using the base equation for a linear equation: 
$$y=mx+c$$
Sub in the known values :
$$y=(0)x+c$$
Simplify 
$$y=c$$
That is the equation of our horizontal line as of now. Now, we know one point on this horizontal line, $B$, and we know the $m$ value of the equation is 0. 
With this information, we can find the equation of the line using the point-slope formula: 
$$y−y_1=m(x−x_1)$$
Where $y_1$ and $x_1$ can be any point on the line. In this case, we will use the $B$ coordinate.
Co-ordinate of B: $(14.99,8.28)$
Let x=14.99 be $x_1$
Let y=8.28 be $y_1$ 
$(14.99,8.28)$=$(x_1,y_1)$
Point-Slope Formula: 
$$y−y1=m(x−x1)$$
Sub in known values: 
$$y−y1=m(x−x1)$$
$$y−8.28=m(x−14.99)$$
$$y−8.28=0$$
$$y=8.28$$
Therefore, the equation that is perpendicular to the directrix, given that one point on that line has the coordinate (14.99,8.28), is y=8.28
