First we write standard form that includes both vertex and focus. The formula goes like this:
(x-h)^2 = 4*p*(y-k)
h and k are coordinates of vertex. since vertex is at beginning that means that h=k=0
p is focal lenght and in our case it is 9
expressing al of this we get:
x^2 = 4*9*y
x^2 = 36y
y = 1/36 * x^2
