Question 326333
The vertex lies halfway between the focus and the directrix.
The vertex is then (0,4).
Use the focus-vertex form of a parabola,
{{{4p(y-k)=(x-h)^2}}}
{{{p}}} is the distance from the focus to the vertex 
{{{p=4}}}
{{{4(4)(y-4)=(x-0)^2}}}
{{{y-4=(1/16)x^2}}}
{{{highlight(y=(1/16)x^2+4)}}}
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{{{drawing(300,300,-10,10,-4,16,circle(0,8,.3),circle(0,4,.3),grid(1),graph(300,300,-10,10,-4,16,(1/16)x^2+4))}}}