Detail solution
Let's take the limit
$$\lim_{n \to \infty} \left(\frac{n}{n + 1}\right)^{3 n + 5}$$
transform
$$\lim_{n \to \infty} \left(\frac{n}{n + 1}\right)^{3 n + 5}$$
=
$$\lim_{n \to \infty} \left(\frac{\left(n + 1\right) - 1}{n + 1}\right)^{3 n + 5}$$
=
$$\lim_{n \to \infty} \left(- \frac{1}{n + 1} + \frac{n + 1}{n + 1}\right)^{3 n + 5}$$
=
$$\lim_{n \to \infty} \left(1 - \frac{1}{n + 1}\right)^{3 n + 5}$$
=
do replacement
$$u = \frac{n + 1}{-1}$$
then
$$\lim_{n \to \infty} \left(1 - \frac{1}{n + 1}\right)^{3 n + 5}$$ =
=
$$\lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{2 - 3 u}$$
=
$$\lim_{u \to \infty}\left(\left(1 + \frac{1}{u}\right)^{2} \left(1 + \frac{1}{u}\right)^{- 3 u}\right)$$
=
$$\lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{2} \lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{- 3 u}$$
=
$$\lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{- 3 u}$$
=
$$\left(\left(\lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{u}\right)\right)^{-3}$$
The limit
$$\lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{u}$$
is second remarkable limit, is equal to e ~ 2.718281828459045
then
$$\left(\left(\lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{u}\right)\right)^{-3} = e^{-3}$$
The final answer:
$$\lim_{n \to \infty} \left(\frac{n}{n + 1}\right)^{3 n + 5} = e^{-3}$$