Chapter 2.2, Problem 21E

Evaluating limits graphically Sketch a graph of f and use it to make a conjecture about the values of $f\left(a\right),\underset{x\to a^{-}}{\lim }f\left(x\right),\underset{x\to a^{+}}{\lim }f\left(x\right),$ and $\underset{x\to a}{\lim }f\left(x\right)$ or state that they do not exist.

  21.     $f\left(x\right)=\{\begin{array}{ll}\sqrt{x}\hfill & \text{if }x<4\hfill \\ 3\hfill & \text{if }x=4\hfill \\ x+1\hfill & \text{if }x>4\hfill \end{array};a=4$