In addition to proposing that planetary orbits are elliptical, what other modification did Kepler make to Copernicus’s model?

What does a triple-beam balance require the user to do? add the numbers from the three sliders to determine the mass of an object multiply the numbers from the three sliders to determine the mass of an object add the numbers from the three sliders to determine the volume of an object multiply the numbers from the three sliders to determine the volume of an object