Derive the equation of the parabola with a focus at (0, −4) and a directrix of y = 4

Derive the equation of the parabola with a focus at (0, −4) and a directrix of y = 4.

A.) f(x) = −16x^2
B.) f(x) = 16x^2
C.) f(x) = −1/16 x^2
D.) f(x) = 1/16 x^2