Answer:
-12x = y^2
Explanation:
Notice that the vertex and the focus are both located on the horizontal line y = 0 (that is, on the x-axis).
Because the focus is to the left of the vertex, we know that the parabola opens left.
The distance between focus and vertex is 3 units.
We'll adapt this equation: 4px = y^2. Here p is -3:
4(-3)x = y^2, or
-12x = y^2