To determine where the graph of $f$ is decreasing, we need to identify the intervals where the slope of the curve is negative (i.e., where the function is going downhill). This happens when the graph is moving downward as $x$ increases.

From the graph, we can observe the following:

1. The first decreasing interval occurs from approximately $x = -8$ to $x = -2$. The graph starts high and decreases until $x = -2$, where it reaches a local minimum.

2. The second decreasing interval is from about $x = 1$ to $x = 4$, where the graph again decreases before reaching another local minimum.

3. The third decreasing interval happens from $x = 6$ to $x = 9$, where the function falls again, reaching a lower point towards the right end of the graph.

Final answer:

The function $f$ is decreasing on the intervals: $(-8, -2), (1, 4), \text{ and } (6, 9).$

Would you like more details on how to find these intervals, or do you have any questions?

Here are 5 related questions for further exploration:

1. How can you mathematically determine the intervals where a function is increasing or decreasing without a graph?
2. What are critical points, and how do they relate to increasing and decreasing intervals?
3. How can we use the derivative of a function to find increasing and decreasing intervals?
4. What is the significance of local maxima and minima in analyzing the behavior of functions?
5. How can concavity and points of inflection help in understanding a function's graph?

Tip: When working with graphs, it's helpful to use the first derivative test to confirm where the function is increasing or decreasing!