\[\begin{split} \lim_{n \to \infty} \frac{1}{5n}+21 &=\lim_{n \to \infty} \frac{1}{5}\cdot \frac{1}{n}+21=\\[16pt] &=\frac{1}{5}\cdot 0+21=\\[16pt] &=0+21=21 \end{split}\]