(b)
Clearly, $f(x)$ is not differentiable at $x = 3$
Now, $\lim_{h \rightarrow 3^{-}}\ f(x) = \lim_{h \rightarrow 0}\ f(3 - h)$
$= \lim_{h \rightarrow 0}\ \ |3 - h - 3|$
$= 0$
$\lim_{h \rightarrow 3^{+}}\ f(x) = \lim_{h \rightarrow 0}\ f(3 + h)$
$= \lim_{h \rightarrow 0}\ \ |3 + h - 3| = 0$
and $f(3) = |3 - 3| = 0$
$\therefore\ \ f(x)$ is continuous at $x = 3$