Answer
$a.\qquad $see image below
$b.\quad (-\infty,\infty)$
$c.\quad $Decreases on$ (-\infty,2.5)$. Increases on $( 2.5,\infty)$
Work Step by Step
$a.$
(graphed with online graphic calculator at desmos.com)
$b.$
$f$ is defined for all reals, $(-\infty,\infty)$
$c.$
f has a minimum at x=2.5.
Decreases on$ (-\infty,2.5)$
Increases on $( 2.5,\infty)$