We have indeterminateness of type
oo/oo,
i.e. limit for the numerator is
$$\lim_{n \to \infty} \left(n + 1\right)^{3} = \infty$$
and limit for the denominator is
$$\lim_{n \to \infty} n^{3} = \infty$$
Let's take derivatives of the numerator and denominator until we eliminate indeterninateness.
$$\lim_{n \to \infty}\left(\frac{\left(n + 1\right)^{3}}{n^{3}}\right)$$
=
Let's transform the function under the limit a few
$$\lim_{n \to \infty}\left(\frac{\left(n + 1\right)^{3}}{n^{3}}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{\frac{d}{d n} \left(n + 1\right)^{3}}{\frac{d}{d n} n^{3}}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{\left(n + 1\right)^{2}}{n^{2}}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{\frac{d}{d n} 3 \left(n + 1\right)^{2}}{\frac{d}{d n} 3 n^{2}}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{6 n + 6}{6 n}\right)$$
=
$$\lim_{n \to \infty}\left(\frac{\frac{d}{d n} \left(6 n + 6\right)}{\frac{d}{d n} 6 n}\right)$$
=
$$\lim_{n \to \infty} 1$$
=
$$\lim_{n \to \infty} 1$$
=
$$1$$
It can be seen that we have applied Lopital's rule (we have taken derivatives with respect to the numerator and denominator) 3 time(s)