To determine the slope of the line using the points given: (3,9), (2,6), (1,3), (0,0), we can use the formula for slope, which is defined as:
\[ \text{slope} = \frac{y_2 - y_1}{x_2 - x_1} \]
We can choose any two points from the line. Let's use the points (0,0) and (3,9):
- \( (x_1, y_1) = (0, 0) \)
- \( (x_2, y_2) = (3, 9) \)
Now, substituting these values into the slope formula:
\[ \text{slope} = \frac{9 - 0}{3 - 0} = \frac{9}{3} = 3 \]
Therefore, the slope of the line is \( \boxed{3} \).