1. The problem asks to estimate the number of CDs sold in 2006 based on the trend from 1999 to 2005 shown in a scatter plot. 2. Since the data shows a decreasing trend over time, a linear model is appropriate to estimate future values. 3. The general formula for a linear function is: $$y = mx + b$$ where $y$ is the number of CDs sold (in millions), $x$ is the year (or time), $m$ is the slope (rate of change), and $b$ is the y-intercept (value when $x=0$). 4. To use this formula, assign numerical values to years, for example, let $x=0$ correspond to 1999, $x=1$ to 2000, and so on. 5. Calculate the slope $m$ using two points from the scatter plot, for example: $$m = \frac{y_2 - y_1}{x_2 - x_1}$$ where $(x_1, y_1)$ and $(x_2, y_2)$ are two known points. 6. Find $b$ by substituting one point into the formula and solving for $b$. 7. Finally, use the formula to estimate $y$ for $x=7$ (which corresponds to 2006). This linear equation will help predict the number of CDs sold in 2006 based on the trend.