* If you completed high school: "Four years" is the most common and straightforward answer.
* If you didn't complete high school: You can answer with the number of years you *did* attend, for example: "Two years," or "Three years." Be prepared to explain why you didn't complete all four years if the question is part of a job application or college application.
* If the question is on a form requiring specific years: Provide the specific years, such as "2018-2022."
* If unsure of how to answer and the context is a job application or college application: Contact the relevant institution for guidance. They will be able to tell you the best format for your response.
In short, be honest and provide the most accurate and relevant information for the situation.