## Algebra: A Combined Approach (4th Edition)

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.