I seem to be blanking on some basic stuff here (doing old homework).

Basically, there is this problem where it asks about the relationship between a roller coasters height (drop) and speed.

Its a classical linear model of 75 roller coasters (scatter plot) with a positive relationship of .91. But here is where I am drawing this blank, I cannot seem to remember how to show that the .91 is not just a coincidence. I am not given mean or median or SD or anything (and having SD wouldn't really help anyway). I started getting these fancy ideas of showing the probability of getting a linear model, which turned into like ($\displaystyle 1/(\infty \div \infty)^{75})$ which was totally stupid, but I was just throwing darts at that point. Can someone take me back to rudimentary stats and remind me how to show low p-value or something, essentially showing a high likelihood of causation.

Thank You