(I apologise if this is in the incorrect section)

I have a stationary points question that I really do not get. I have worked out that the SP's are (0,0) and (2,-4), but I do not know how to find Q.

Question:

Part of the graph of the curve with equation is shown below.

(I used a graphic calculator online to draw the graph)

a) Establish the coordinates of the stationary point P.

b) The horizontal line through P meets the curve again at Q. Find the co-ordinates of Q.

So far, I have worked out the SPs:

or

or

When x=0, y=0, point(0,0)

When x=2, point(2,4) (which is P).

But I don't know how I'm supposed to find Q. Can anyone please help?

Thanks in advance