See this.
I prefer the definition I used because I can get equations for parabolas with axes of symmetry that aren't "nice."
In any event the directrix here is parallel to the y axis, so we can use the form
p is the twice the distance between the directrix and the focus, so p = 4. The vertex is half way between the directrix and the focus so it is at V(2, -10). So the equation will be
Finally, we know that the focus is to the right of the directrix, so this parabola opens to the right. Thus we choose the + sign:
Edit:
You can solve for the answer using my method:
-Dan