To find the equation of the line \(y = mx\) that describes the proportional relationship shown in the graph, we first need to determine the slope \(m\) of the line that passes through the points \((1, 4)\) and \((2, 8)\).
The slope \(m\) is calculated using the formula:
\[ m = \frac{y_2 - y_1}{x_2 - x_1} \]
Substituting the coordinates of the points:
- \((x_1, y_1) = (1, 4)\)
- \((x_2, y_2) = (2, 8)\)
we can calculate the slope as follows:
\[ m = \frac{8 - 4}{2 - 1} = \frac{4}{1} = 4 \]
Now that we have determined that the slope \(m\) is 4, we can write the equation of the line:
\[ y = 4x \]
Thus, the equation of the line that describes the proportional relationship shown in the graph is:
\[ \boxed{y = 4x} \]