The vertex form of the equation of a vertical parabola is given by y = 1/4p (x- h)^2 + k, where (h, k) is the vertex of the parabola and the absolute value of p is the distance from the vertex to the focus, which is also the distance from the vertex to the directrix. If I mark the focus of the parabola at F(6, 4) and draw a horizontal line that is 6 units below the focus, what is the equation of the line?