the graph is a horizontal parabola, that means, the squared variable is the "y", so it looks like x = y².... and so on.
now, is opening towards the left-hand-side, that means, the leading term's coefficient is negative, so, the only function there, which is in term's of a y² with a negative coefficient, is x = -y² +2y + 5.
you can always try graphing it in your graphing calculator, to check about.
