The question asks for the constant of proportionality between $y$ and $x$ in the given graph.

Step-by-Step Solution:

1. Identify a point on the graph: A clear point on the graph is $(2, 3)$. This means when $x = 2$, $y = 3$.

2. Proportional relationship formula: In a proportional relationship, $y = kx$, where $k$ is the constant of proportionality.

3. Find $k$: $k = \frac{y}{x}$ Substituting $y = 3$ and $x = 2$: $k = \frac{3}{2}$

Thus, the constant of proportionality is: $\boxed{\frac{3}{2} \text{ or 1.5}}$

If you have further questions or want additional clarification, feel free to ask! Here are five related questions to explore this concept further:

1. How do you verify that a graph represents a proportional relationship?
2. Can the constant of proportionality ever be negative?
3. What is the meaning of the constant of proportionality in a real-world context?
4. How can you determine the constant of proportionality from a table instead of a graph?
5. What happens to the constant of proportionality if the scale of the axes changes?

Tip:

When working with proportional relationships, always check if the ratio $\frac{y}{x}$ remains constant for all points on the graph!