Evaluate the limits. $$f(x) = \begin{cases} \dfrac{|3 x|}{x} & x \neq 0 \\ 0 & x = 0 \end{cases}$$ Enter DNE if the limit does not exist.

1. $\displaystyle{ \lim_{x \to 0^-} f(x) = }$
2. $\displaystyle{ \lim_{x \to 0^+} f(x) = }$
3. $\displaystyle{ \lim_{x \to 0} f(x) = }$
4. $\displaystyle{ f(0) = }$