Which is the directrix of a parabola with equation x^2=y

now, notice, the vertex is at h = 0, k = 0, or 0,0, at the origin, the squared variable is the "x", and thus is a vertical parabola.  The leading term's coefficient is positive, so is going upwards, and the "p" distance is that much.

So the directrix is from the vertex, down "p" distance, check the picture below.

It’s 8.99 for john hub b