1. Let's clarify the terms first. 2. A **proportional relationship** is when two quantities change in such a way that their ratio remains constant. For example, if $y$ is proportional to $x$, then $\frac{y}{x} = k$ for some constant $k$. 3. This can be expressed mathematically as $$y = kx$$ where $k$ is the constant of proportionality. 4. For example, if the cost is proportional to the number of items bought, and each item costs $5$, then $$\text{cost} = 5 \times \text{number of items}$$. 5. The **cost of proportion** is not a standard term in math, but it might refer to the actual cost value calculated using a proportional relationship. 6. In summary, a proportional relationship describes how two quantities relate with a constant ratio, while the cost calculated through this relationship is the actual value obtained by multiplying the proportion constant by the quantity.