In Harold Jacobs Geometry we skipped over material is chapters 12, 13, 15, and 16 because
1. It is not needed for ACT/SAT nor future math classes, and
2. it is a overly complex for the course at this level.
Our recommendation is that the student look over this material and get the idea – but move on. You will find a test problem that points back to some of this material in a trivial way, but we decided to leave it in as a learning tool since often in life we find ourselves having to dig a little to get to an answer – even when being tested. Since we recommend open book tests, this usually works well. And, just in case, it is only one problem and the teacher can decide to skip it if they like.
For 19 you can get a line of symmetry between each one that is hand to hand (wing to wing) and each one that is nose to nose. Those total 7. In other words, you can make a fold in many places if you take two at a time (or individuals which is what the problem asks).
For 20 assume you cut two penguins at once (those wing-to-wing) So the folds to get what w have on this page is 2, once in the middle, then fold that one more time to get four patterns of two penguins each.
To get 16, double that.