Aparabola can be represented by the equation y2 = 12x.
which equation represents the directrix?
y = –3
y = 3
x = –3
x = 3

The given equation of parabola is :

As ,

Focus = (3,0)

Vertex = (0,0)

Distance from focus to Parabola = Distance of Directrix from parabola = 3

But Directrix will lie on negative X axis.i.e at (-3,0).

Equation of line parallel to y axis and passing through (-3,0) is :

: x = -3→ Option 3  

for the friend request.

when a figure, such as triangle (xyz) is reflected over the line y = x to create x'y'z' the x-coordinates and y-coordinates of the original image (pre-image) will be reversed for the image. (e.g., (x, y) > (y, x)) this means that the pre-image position of the x- and y-coordinates switch places which in turn provides a mirror like image of the original xyz.  

i notice that when i draw a line segment from x to x', that the points are parallel from each other -- they are exactly across from each other and do not intersect with any other points.  

yes, think i would see the same characteristic if you drew the line segment connecting y with the reflecting line and then y' with the reflecting line because of the essence of reflections. because it is a mirror image, each point was effected the same way which leads me to conclude that they same would apply to y and y'.