Find the centroid of the triangle formed by the feet of the three normal lies on the axis of parabola?

Question

$\begin{array}{1 1}(a)\;(\large\frac{2h-4a}{3},\normalsize 0)\\(b)\;(\large\frac{2h-2a}{3},\normalsize 1)\\(c)\;(\large\frac{3h-4a}{3},\normalsize 3)\\(d)\;(\large\frac{2h+4a}{3},\normalsize 1)\end{array}$