Hi
the vertex form of a Parabola opening right(a>0) or left(a<0), 

where(h,k) is the vertex and y = k is the Line of Symmetry,
the focus is (h +p,k ), With Directrix x = (h - p) , a = 1/(4p)

V(0,0) F(-3/2,0)  Opens Left:  p =   a = (-1/6)

x = (-1/6)y^2, the vertex form of a Parabola
Wish You the Best in your Studies.