Calculus with Applications (10th Edition)

$\displaystyle \lim_{x\rightarrow 4^{-}}f(x)=\lim_{x\rightarrow 4^{+}}f(x)=6,\ \ \ \$ so both the limits from the left and from the right exist, and, they are equal, which means that $\displaystyle \lim_{x\rightarrow 4}f(x)$ exists and $\displaystyle \lim_{x\rightarrow 4}f(x)=6$.