Hi =)
I think the way to solve this is by plotting on the enzyme concentration on the Y-axis, and on the X axis the rxn rate. But to do that, you need to graph first the substrate concentration versus time (here most probably you would get a straight line because as I see on the results, the more subrstrate, the more time), in order to get the reaction rate to THEN plot it against enzyme concetration. You should obtain some sort of line or curve ( most probably a curve). Draw the best fit line or curve. You might end up with Y=x2 or y=x or y=root X or perhaps an exponential graph. Maybe even get a direct proportionality or inverse proportionality, depending on the graph you obtain, and the mathematical representation that corresponds to the graph.
For discussing the relation, this is a conceptual question. It is testing how well you grasped the concept of how enzymes work. Now since it is a dilution of saliva, we expect the salivary glands to increase enzyme secretion ( higher concentration) upon ingestion of food. So it will rise for a certain time, reaching a climax, and then drop sequentially as food is no longer ingested. You see where I am going? So maybe, as food conc. increases, enzyme conc increase, and when food conc. decreases, enzyme conc. decreases. Here you've got a direct proportionality. Discuss your results= write everything you know and could think of. =P That's what I do in my labs, and most of the time, I get the full grade
Good luck!