Find the standard form of the equation of the parabola with a focus at (3, 0) and a directrix at x = -3.

Check the picture below.

now, keep in mind that the focus point is at 3,0 and the directrix is to the left-hand-side of it, therefore, is a horizontal parabola, and it opens to the right-hand-side, like in the picture.

keep in mind that the vertex is half-way between the focus point and directrix, at a distance "p" from either one, notice the "p" distance is just 3 units, since the parabola is opening to the right, "p" is positive.