We have indeterminateness of type
oo/oo,
i.e. limit for the numerator is
$$\lim_{n \to \infty}\left(4 n\right) = \infty$$
and limit for the denominator is
$$\lim_{n \to \infty}\left(n - 1\right) = \infty$$
Let's take derivatives of the numerator and denominator until we eliminate indeterninateness.
$$\lim_{n \to \infty}\left(\frac{4 n}{n - 1}\right)$$
=
Let's transform the function under the limit a few
$$\lim_{n \to \infty}\left(\frac{4 n}{n - 1}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{\frac{d}{d n} 4 n}{\frac{d}{d n} \left(n - 1\right)}\right)$$
=
$$\lim_{n \to \infty} 4$$
=
$$\lim_{n \to \infty} 4$$
=
$$4$$
It can be seen that we have applied Lopital's rule (we have taken derivatives with respect to the numerator and denominator) 1 time(s)