The graph of a function $f$ is shown below.

At which of the labeled $x$-values is
$f(x)$ least? $x =$ ? x1 x2 x3 x4 x5 x6
$f(x)$ greatest? $x =$ ? x1 x2 x3 x4 x5 x6
$f'(x)$ least? $x =$ ? x1 x2 x3 x4 x5 x6
$f'(x)$ greatest? $x =$ ? x1 x2 x3 x4 x5 x6