Answer
$a.) m=135$
$b.) m=0$
$c.)m=-40$
Work Step by Step
$a.) m=135.$ The sales are increasing at a rate of 135 units per year.
$b.) m=0.$ There is no change in sales during the year.
$c.) m=-40.$ The sales are decreasing at a rate of 40 units per year.
