In this experiment, they want to test the effect of each wax, with the question being "which wax protects the floor the most from scratches?" or "with which wax does the floor has the least scratches?"
The independent variable depends only on itself and is not affected by others, in this case, it would be the type of wax (expensive, cheap, none).
The dependent variable is the one that would change with the independent variable, in this case, the number of scratches.
The constants would be things that don't change, in this case, the size of the sections, and the kind of tiles.