Check the picture below. So the parabola looks like so.
we know the directrix is at x = 11.25, the blue line, and we also know the focus point is at (6.75 , 6), meaning that the focus point is to the left-side of the directrix, it means is a <u>horizontal parabola, thus the squared variable is the "y"</u>, and it also means that our "p" distance will be negative.
we know the <u>the vertex is half-way between the directrix and the focus point</u>, so 11.25 - 6.75 = 4.5, half that is 2.25 units, so if we move from either the focus point or the directrix, 2.25 units towards the other, we'll get the vertex, well, hmmm say 11.25 - 2.25 = 9, and the y-coordinate is of course the same as the focus point's.
now, since "p" is negative, that means p = -2.25.