Question

which two variables are used to find the density of a substance? length and width mass and volume

Explanation:

The formula for density is $
ho = \frac{m}{V}$, where $
ho$ is density, $m$ is mass, and $V$ is volume. Length and width are used to calculate area (for 2D) or part of volume (for 3D like length×width×height for rectangular solids), but not directly for density. So mass and volume are the variables for density.

Answer:

mass and volume