Since it passes though (-4,-6), then it opens either left or downward, but since it is parallel to the x-axis, then it opens to the left. The equation of the parabola that opens to the left with vertex at the origin is:
You are given the coordinates, use the coordinates to find a by substituting.
Substitute the value of a in the equation.
The equation of the parabola is y²=18x. Hope this helps =)