BSOSF

okay i have to make a scientific inquiry for school, im a freshman. i think i have my experiment figured out so far, im doing it on fresh vs salt rusting. Question is: Which causes metal (nails) to rust faster; saltwater or freshwater?
Hypothesis: im guessing freshwater, but i dont know why just seems good to me.
what do you think and why?
*i also need to come up with a graph* but i dont know how i should do it. HELP PLEASE

It's saltwater. The certain chemicals in most metals tend to react with sodium more violently than simply H2O.
For the graph, you could use amount of rust as a function of time.