You can put this solution on YOUR website!
"What is the equation of the vertical line that passes through the point (0,4)?
This is a special case, vertical lines have the equation of x=k. Where k is the x value of any point the line goes through.
So the equation of the vertical line going through that point is: x=0
That is a special vertical line known also as the y-axis.
If they had of asked for the equation of the vertical line going through (5,3), the answer would have been x=5.
I hope things are clearer.