Which is the equation of a parabola with vertex (0, 0) and directrix y = 4?

We know that

Vertex (0, 0) and directrix y = 4

is a vertical parabola------> open down (directrix above the vertex)
the equation is of the form
(y-k)=4p(x-h)²--------> y=4p*x²-------> vertex (0,0)

y=4
y=h-p-----> y=-p
p=-4

the equation of the parabola is
y=-16x²

the answer is
y=-16x²

see the attached figure