So,
1. From the graph, we can see a line that passes through the origin. Two quantities that are in direct proportion will always produce a straight-line graph that passes through the origin, so the graph indicates a proportional relationship.
2. From the graph, we can notice that there's a ratio whose value is constant and it is 5. Direct proportion is the relationship between two variables whose ratio is equal to a constant value, so that's other reason that make us notice that the graph indicates a proportional relationship.
