[tex]\mathbf x(t)=\langle -9,-3,t\rangle[/tex]
should do it. The [tex]x[/tex] and [tex]y[/tex] coordinates of any point on the line are fixed, and since only the [tex]z[/tex] coordinate changes, this line is vertical. And of course, when [tex]t=9[/tex], the line passes through the point [tex](-9,-3,9)[/tex].
