One strategy for Amazing Alex The Backyard level 2-4, called “Ball Crossing”, is to extend the pipping along the two middle elbows. This should guarantee obtaining the top star. Place two pipes, angled slightly inward, just below each of the remaining two stars to guide the outside 8-balls. If you are having trouble keeping the billiard balls in the playing area, use elbow joints to block escape paths.
If you have a different strategy for completing this level feel free to leave a comment below.