Find the X-Value at Which the Given Function Has a Point

Multiple Choice

Find the x-value at which the given function has a point of inflection. $y = \frac { 1 } { 3 } x ^ { 3 } - 4 x ^ { 2 } + 15 x + 9$

A) $x = 0$
B) $x = 5$
C) $x = 4$
D) $x = 3$
E) no point of inflection