Let $f(x)=\{\begin{array}{ccc}-\frac{21}{x}& if& x<mn>3</mn>\\ \frac{28}{x-7}& if& x>3\end{array}$

Compute the quantities below. Write "DNE" if the limit does not exist or the value is undefined.

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

$\underset{x{3}^{}}{lim}f(x)=$

$f(3)=$

$$

$$

Since the above three quantities are $$ Select an answer $,$ we know that $f$ is $$ at $x=3.$

List ALL numbers at which $f$ is discontinuous. Be sure to check the functions defined to the left and right of $3$ for discontinuities.