Final answer:
Chapter 9 of TC 21-305-20 is a chapter within a U.S. Army manual.
Step-by-step explanation:
Chapter 9 of TC 21-305-20 is a chapter within a military science manual, which may not be directly related to any specific academic subject such as Mathematics or History. However, TC 21-305-20 is a U.S. Army manual titled "Manual for the Wheeled Vehicle Driver." Therefore, Chapter 9 of TC 21-305-20 would likely cover a specific topic related to driving wheeled vehicles in the military.