Two points P(6,8) and Q(24,16) are suspected to lie on the same parabola of the form y2=4ax.
(i) Using the coordinates of P, determine the value of a.
(ii) Verify whether the same value of a also satisfies the coordinates of Q.
(iii) If your verification in part (ii) is affirmative, find the abscissa(s) of the point(s) on the parabola whose ordinate is −8.