Remy should test the relationship between the height of the mountain and the size of the tsunami wave by performing the following experiment:
Build different-sized model mountains at the edge of a pool, pour sand down the side of each mountain, and see how large each resulting wave is.
This method allows Remy to systematically vary the height of the model mountains while keeping other factors constant, enabling a direct comparison of the height of each mountain to the size of the resulting waves.