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
