Credits and licences for the narrated videos
Preparing for Algebra and Statistics, Third Edition (XYZ Homework Edition), by Matt Teachout

Who made the videos
XYZ Homework made these narrated videos for its edition of the book. Each video works an example from the book step by step on screen, pauses so you can think before the answer is shown, and comes with English captions and a transcript. The XYZ Crunch demonstration in Section 2G is a screen recording of XYZ Crunch, a statistics tool made by XYZ Homework.

The book and its licence
The videos are adapted from Preparing for Algebra and Statistics, Third Edition, by Matt Teachout, College of the Canyons, Santa Clarita, California: https://matt-teachout.org/pre-stats/
The book is licensed under the Creative Commons Attribution 4.0 International licence (CC BY 4.0): https://creativecommons.org/licenses/by/4.0/
Changes were made: XYZ Homework wrote the narration and the on-screen steps, and added the captions and transcripts. The videos are shared under the same licence, CC BY 4.0. The licence does not cover trademarks, and it does not mean that the author endorses these videos.

The narration
The narration is synthetic: it is a computer-generated voice, not a recording of a person. XYZ Homework generated it offline, on its own computers, with the Kokoro-82M text-to-speech model, version 1.0, using the voice named af_heart.
Kokoro-82M and its code are licensed under the Apache License, Version 2.0.
Model card, with the model's training acknowledgements: https://huggingface.co/hexgrad/Kokoro-82M
About the af_heart voice: https://huggingface.co/hexgrad/Kokoro-82M/blob/f3ff3571791e39611d31c381e3a41a3af07b4987/VOICES.md
Licence: https://github.com/hexgrad/kokoro/blob/main/LICENSE
The model card credits Li et al. for StyleTTS 2, the design Kokoro is built on (https://github.com/yl4579/StyleTTS2). It also lists Creative Commons audio among the model's training data: Koniwa, CC BY 3.0 (https://github.com/koniwa/koniwa), and SIWIS, CC BY 4.0 (https://datashare.ed.ac.uk/handle/10283/2353).