Aparabola has a vertex at the origin. the equation of the directrix of the parabola is y = 3. what are the coordinates of its focus? (0,3) (3,0) (0,–3) (–3,0)

The vertex is halfway between the focus and the directrix. If the directrix is a line 3 units above the origin, the focus will be a point 3 units below the origin, at
  (0, -3)