Answer
This slope means that every year, there's a 12 billion dollar increase in sales.
Work Step by Step
Slope $= \frac{\delta y}{\delta x}$
Slope $= \frac{240-120}{1990-1980}$
Slope $= \frac{120}{10}=\frac{12}{1}=12$
$y$ is the number of sales.
$x$ is the year.
This slope means that every year, there's a 12 billion dollar increase in sales.
