Use the rules for convergent scquences to evaluate the following limits:
(a) $\lim _{n \rightarrow \infty} \frac{4 n^{3}+6 n-7}{n^{3}-2 n^{2}+1}$
(b) $\lim _{n \rightarrow \infty} \frac{6-n^{2}}{n^{2}+5 n}$
(c) $\lim _{n \rightarrow \infty}\left[\log _{e}(n+1)-\log _{e} n\right]$