\item{4.}
\itemitem{a.}  Suppose that $x_n \to e$ (the base of the natural logarithms).  Explain why there exists
an $n_0$ such that $x_n < 3$ for all $n \ge n_0$.
\itemitem{b.}  Suppose $x_n \to 6$ and $y_n \to 9$.  Explain why there exists an $n_0$ such that
$x_n + y_n > 14$ for all $n \ge n_0$.
