Vertex A(0,0) ; focus S(3,0)
Since, the vertex of the parabola is (0,0) and the focus lies on the positive x-axis , so the axis of the parabola is x-axis.
Equation of the parabola is of the form y2=4ax
Since, the focus is (3,0), so a=3
Thus, the equation of the parabola is y2=12x