$($For each given limit$,$ if the numerical value of the limit exists, enter the answer as an integer or as a simplified fraction in lowest terms; if the limit doesn't exist, enter "DNE" in uppercase.$)$

Let

$($a$)$ Find $\underset{x-3^{-}}{lim}f(x)=?$

$($b$)$ Find $\underset{x-3^{+}}{lim}f(x)=?$

$($c$)$ Find $\underset{x-3}{lim}f(x)=?$