Our parabola equation is (after playing with the equation a little)
[tex]-\frac{1}{24}y^2\text{ = x}[/tex]It is a horizontal parabola extending to the left side (because of the minus). Then, the focus (F) is a point (an ordered pair (a,b)) inside the area covered by the parabola (with this in mind is easy to answer the question, for the only point that satisfies this is (-6, 0)) that satisfies
[tex]F\text{ = (}\frac{1}{4(-\frac{1}{24})},0\text{) = (-6, 0)}[/tex]On the other side, after knowing the value of the focus, the directrix of this parabola must have the form
[tex]x\text{ = -(-6) =6}[/tex]