Find the Largest Open Intervals Where the Function Is Concave $f(x)=-3 x^{2}+18 x+16$

Multiple Choice

Find the largest open intervals where the function is concave upward.
- $f(x) =-3 x^{2}+18 x+16$

A) $(3, \infty)$
B) None
C) $(-\infty, \infty)$
D) $(-\infty, 3)$