1. The problem states there is a proportional relationship between the size of Zane's garden $x$ (in square feet) and the number of carrots $y$ he can grow. 2. A proportional relationship means $y = kx$, where $k$ is the constant of proportionality. 3. From the graph, two points on the line are $(1, 2)$ and $(5, 10)$. 4. To find $k$, use the formula for constant of proportionality: $$k = \frac{y}{x}$$ 5. Using the point $(1, 2)$: $$k = \frac{2}{1} = 2$$ 6. Using the point $(5, 10)$: $$k = \frac{10}{5} = 2$$ 7. Both points give the same $k = 2$, confirming the constant of proportionality. 8. Therefore, the constant of proportionality is $2$. Final answer: $2$