To determine the constant of proportionality (unit rate) from a graph, you typically need to look at the ratio of the change in the y-axis (vertical) to the change in the x-axis (horizontal).
If, for example, the graph shows that for every increase of 1 on the x-axis, the y-axis increases by 3, then the constant of proportionality would be 3 over 1, which simplifies to 3. If the graph shows the y-axis increasing by 1 for every 3 on the x-axis, the constant would be 1/3.
Without seeing the specific graph, I can't definitively tell you which response is correct. Please review the graph to identify the correct ratio. If the graph indicates that for every 1 unit increase on the x-axis there is a 3 unit increase on the y-axis, the answer would be 3. If it's the reverse (for every 3 unit increase on the x-axis there is a 1 unit increase on the y-axis), it would be 1 third.