Let $f(x)$ be a function that is defined and has a continuous derivative on the interval $(2, \infty )$. Assume also that $$f(3) = 7$$ $$|f(x)| < x^{9} + 3$$ and $$\int_{3}^{\infty} f(x) e^{-x/3} \,dx = 1$$

Determine the value of $$\int_{3}^{\infty} f'(x) e^{-x/3} \,dx$$