What is the equation of a parabola with Vertex (0 0) and focus (-3 0) a.y2-4x b.y2-12x c.y24x d.y212x?

The equation of a parabola with a vertex at the origin (0, 0) and a focus at (-3, 0) opens to the left. The standard form for such a parabola is ( y^2 = -4px ), where ( p ) is the distance from the vertex to the focus. Here, ( p = 3 ), so the equation becomes ( y^2 = -12x ). Therefore, the correct answer is b) ( y^2 = -12x ).