Answer
(a) See the image below.
Work Step by Step
As we can see on the image $y=e$ is a line (a number) which the graph of $y=(1+\frac{1}{x})^x$ approaches "infinitely" close but not actually gets to it.
We also have a term for it which is $Asymptote$ (Also explained in later chapters). In this case we have $Horizontal Asymptote$.
In short $e$ is a limit (*also explained later in calculus) of the function $f(x)=(1+\frac{1}{x})^x$ as $x$ approaches infinity.