For a differentiable function \( f:\mathbb{R} \to \mathbb{R} \), suppose \( f'(x) = 3f(x) + \alpha \), where \( \alpha \in \mathbb{R} \), \( f(0) = 1 \) and \(\displaystyle \lim_{x \to -\infty} f(x) = 7 \). Then \( 9 f(\ln 3) \) is equal to ________.
