The Vertex of a Parabola Occurs Where the Derivative of Its

The vertex of a parabola occurs where the derivative of its equation is 0, so an equation associated with the equation of a
parabola can be solved to find the x-coordinate of the vertex. Find the vertex of the parabola, given the equation of the
parabola and its associated equation.
-Between $x = 0$ and $x = 8$ , the largest value of the expression $y = x ^ { 3 } - 15 x ^ { 2 } + 63 x + 18$ occurs where $3 x ^ { 2 } - 30 x + 63 = 0$ . Of the values of $x$ that satisfy $3 x ^ { 2 } - 30 x + 63 = 0$ , which gives the maximum value of $y = x ^ { 3 } - 15 x ^ { 2 } + 63 x + 18 ?$

A) $x = 2$
B) $x = 3$
C) $x = 6$
D) $x = 7$