We have indeterminateness of type
oo/-oo,
i.e. limit for the numerator is
$$\lim_{x \to \infty} x^{4} = \infty$$
and limit for the denominator is
$$\lim_{x \to \infty}\left(- x^{2} + 9\right) = -\infty$$
Let's take derivatives of the numerator and denominator until we eliminate indeterninateness.
$$\lim_{x \to \infty}\left(\frac{x^{4}}{- x^{2} + 9}\right)$$
=
$$\lim_{x \to \infty}\left(\frac{\frac{d}{d x} x^{4}}{\frac{d}{d x} \left(- x^{2} + 9\right)}\right)$$
=
$$\lim_{x \to \infty}\left(- 2 x^{2}\right)$$
=
$$\lim_{x \to \infty}\left(\frac{\frac{d}{d x} 4 x^{3}}{\frac{d}{d x} \left(- 2 x\right)}\right)$$
=
$$\lim_{x \to \infty}\left(- 6 x^{2}\right)$$
=
$$\lim_{x \to \infty}\left(- 6 x^{2}\right)$$
=
$$-\infty$$
It can be seen that we have applied Lopital's rule (we have taken derivatives with respect to the numerator and denominator) 2 time(s)