The given equation is:

$115 = k(25)$

This represents a direct variation where $k$ is the constant of proportionality. To find $k$, we need to solve for $k$:

$k = \frac{115}{25}$

Let's calculate that:

$k = \frac{115}{25} = 4.6$

Thus, the constant of proportionality $k$ is 4.6.

Would you like more details or have any other questions?

Here are five related questions to expand on this concept:

1. How do you interpret the constant of proportionality in a real-world problem?
2. What are the units of the constant of proportionality if we are given units for 115 and 25?
3. Can you graph a direct variation relationship, and what does the slope represent in this case?
4. How would the equation change if the value of $115$ were doubled?
5. How does solving for $k$ differ in inverse variation problems?

Tip: In any proportional relationship, the constant $k$ remains the same as long as the relationship between the variables doesn't change.