Thanks for the question! I would set this one up in a pretty straightforward manner. You can draw six lines in a vertical (or technically in a horizontal) manner, and then diagram the rules:
R > W
>=1G under all Rs ?G?W
And then from here you can think about implications of these rules and then move on to the questions. For example, you can think about what happens if there are two white balls: then there have to be three red balls, and thus one green ball. Or if there’s only one white ball, then there are more possibilities.
Hope this helps! Feel free to ask any other questions that you might have.