Equation of the Vertical Line

Write an equation of the vertical line passing through the point (8,5).

Vertical for you and vertical for me may not be same. So there must be some wrong wording.
Did you mean parallel to y-axis? Then it is x=8 but then what do you call a line parallel to z-axis as?Slant or horizontal or neither?Use appropriate terminology by thinking to yourself.

VERTICAL line, you say?

Well, since it's a vertical line, the gradient (which is equal to the change in y/change in x) will be undefined or zero, because there is no change in the x-axis.

So, the equation of a straight line is in the form y=mx + c (where m is the gradient of the line and c the y-intercept)
Therefore, the equation for the vertical line passing through (8,5) will be: y=5

x equals 5 is the equation

x = 8