1. The problem asks for the slope of the line that relates the number of cubes dropped into the container ($x$) to the volume of water in the container ($V$). 2. From the graph description, the line passes through the points $(0, 8)$ and $(3, 20)$. 3. The slope $m$ of a line passing through points $(x_1, y_1)$ and $(x_2, y_2)$ is given by: $$m = \frac{y_2 - y_1}{x_2 - x_1}$$ 4. Substitute the points: $$m = \frac{20 - 8}{3 - 0} = \frac{12}{3} = 4$$ 5. Therefore, the slope of the line is $4$. This means that for each cube dropped into the container, the volume increases by 4 milliliters.