I was very happy to see many new “puzzle solvers” for this puzzle. I was particularly impressed with Aadi Kuchlous and Sahil Kuchlous who solved the 6 and the 9 balls puzzle respectively. Same is true for Arushi and Anisha Goyal. Many adults gave the correct answer for the 12 balls puzzle.
Answer to the first two parts is simple and is in the video link.
For the 12 balls puzzle, there are many different ways to solve. I have given one way to solve in the video link, but I would highly encourage you to look at the different ways. I did not realize that there is so much science in this puzzle! Look at the following link for a more complete treatment of this puzzle.
Hope you enjoyed this!