Answer
a) $-\infty$
b) $x=4$
c) The vertical asymptote exists where the limit does not exist.
Work Step by Step
a) As we can see from the graph, when approaching the value $x = 4$ from both LHS and RHS, the value of $f(x)$ tends to infinity.
b) The value of $f(x)$ approaches infinity when $x$ gets close to $4$. The vertical asymptote is:
$x=4$
c) The vertical asymptote exists where, for a particular $x$-value, a corresponding $y$-value does not exist. It is where one could draw a vertical straight line on the graph with it not touching the function. Here, it exists at $x = 4$.
