Final answer:
Based on the information provided, it is not possible to determine the average increase in premium when a teen is added to their parents' policy in NYS.
Step-by-step explanation:
The question asks about the average increase in premium when a teen is added to their parents' policy in NYS. However, the information provided in the prompt is not relevant to directly answer this question. It discusses the mean annual cost of auto insurance for teenage boys and girls, but not the average increase when a teen is added to their parents' policy.
Therefore, it is not possible to determine the NYS' average increase in premium based on the given information.