Question 828973
The standard form is {{{(x - h)^2 = 4p (y - k)}}} and the directrix is {{{y = k - p}}}.

The standard form of a parabola is:
{{{(x - h)^2 = 4p (y - k)}}}
where (h,k) is the vertex.
{{{x^2 = 4py}}}
The directrix is 
{{{y = k - p=-3}}}
{{{0-p=-3}}}
{{{p=3}}}
So then,
{{{x^2 = 4py}}}
{{{x^2 = 12y}}}
{{{highlight(y=(1/12)x^2)}}}