Let \( f : \mathbb{R} \to (0,\infty) \) be a twice differentiable function such that \( f(3)=18 \), \( f'(3)=0 \) and \( f''(3)=4 \). Then
\( 9 \)
\( 1 \)
\( 18 \)
\( 2 \)
