tangent parallel to y or x axis

Find the critical points for each of the following. Determine whether the critical point is a local max or min and whether or not the tangent is parallel to the horizontal axis.

y=(-x^2)(e^(-3x))

so i had no problem finding the critical points and max or min points, but I am wondering about whether or not the tangent is parallel to the horizontal axis.

In the back of the book the answer says:

(0,0) is a local max, tangent parallel to the t-axis, (2/3, -4/(9e^2)) is a local min, tangent parallel to t-axis.

Ok, I am thinking that t-axis is a typo and supposed to be y-axis for both cases. BUT, I am not sure why this is true (both parallel to the y-axis).

When I graph it, they both look parallel to the x-axis to me. How do you know if it is parallel to y-axis?