Question

What is the directrix of the parabola defined by (x + 3)2 = -20(y − 1)?

Answer 1

we have that

(x + 3)² = -20(y − 1)
This is actually the vertex form, so we can obtain the vertex already
the vertex is the point (h,k)------------> (-3,1)

4p=-20------------> p=-5
Focus is at (-3,1-5)---------> (-3,-4)
Directrix is at y = 1-(-5)----------> y=6

the answer is
the directrix is y=6

see the attached figure