Answer
$a.\quad -0.8$
$b.\quad $
$0.8, $
$ 0.8\%$ per year
Work Step by Step
Use: $m=\displaystyle \frac{\text{change in y}}{\text{change in x}}=\frac{y_{2}-y_{1}}{x_{2}-x_{1}}$
$(a)$
The slope of the line passing through $(22,49)$ and $(62,29)$ is
$m_{1}=\displaystyle \frac{29-49}{62-49}=\frac{-20}{25}\cdot\frac{4}{4}=-\frac{80}{100}=-0.8$
$(b)$
The slope written as $\displaystyle \frac{\text{change in y}}{\text{change in x}}=\frac{-0.8}{1}$
is interpreted as:
For a 1 year change in x, stress (y) decreases by $ 0.8\%$.
The unit for slope is (unit for y)/(unit for x).
Here: "percent per year"
