A. $5$A. $5$ B. $3$ C. $15$ D. $\displaystyle \frac{1}{5}$ E. $1$
1. When a line passes through the origin, $\left(0, \; 0\right)$, the line represents a proportional relationship between $x$ and $y$. The unit rate is $r$ when the line passes through $\left(1, \; r\right)$. Because the point $\left(3, \; 15\right)$ is on the graph, the point $\displaystyle \left(1, \; \frac{15}{3}\right) = \left(1, \; 5\right)$ is also on the graph. Therefore, the unit rate is $5$. No More Steps
