We have indeterminateness of type
0/0,
i.e. limit for the numerator is
$$\lim_{x \to \infty} \frac{1}{\left(x + 1\right)!} = 0$$
and limit for the denominator is
$$\lim_{x \to \infty}\left(\frac{1}{y x!}\right) = 0$$
Let's take derivatives of the numerator and denominator until we eliminate indeterninateness.
$$\lim_{x \to \infty}\left(\frac{y x!}{\left(x + 1\right)!}\right)$$
=
Let's transform the function under the limit a few
$$\lim_{x \to \infty}\left(\frac{y x!}{\left(x + 1\right)!}\right)$$
=
$$\lim_{x \to \infty}\left(\frac{y x!}{\left(x + 1\right)!}\right)$$
=
$$0$$
It can be seen that we have applied Lopital's rule (we have taken derivatives with respect to the numerator and denominator) 0 time(s)