Final answer:
The characteristic not found in adolescents working more than 20 hours a week is improved financial literacy; instead, these adolescents often have increased substance use, lower academics, and higher stress levels.
Step-by-step explanation:
The characteristic of adolescents who work more than 20 hours per week that has not been found is c) Improved financial literacy. Research on the subject does indicate that working such hours can lead to increased substance use, lower academic achievement, and higher levels of stress. These effects are documented because adolescents working long hours often struggle to balance work and school, leading to negative outcomes such as getting bad grades, truancy, dropping out, not graduating, and difficulty finding suitable employment post-graduation. Furthermore, the stress related to juggling work with other responsibilities may contribute to higher stress levels, as noted in national surveys tracking stress over time.