Answer:
x = 4
Step-by-step explanation:
Since the two points (-1, 14) and (9, 14) lie on the same horizontal line y = 14,
and intersects this parabola. We know by symmetric property of the parabola that the line of symmetry goes through the midpoint of (-1, 14) and (9,14)
at x = (-1 + 9)/2 = 8/2 = 4
at x = 4 is our line of symmetry
