A vertical blue line in the graph. What is the equation of the line?

Please directly answer the question and provide the final value, e.g., 1, 2.5, 300.
Question: A vertical blue line in the graph. What is the equation of the line?

Please first conduct reasoning, and then answer the question and provide the final value, e.g., 1, 2.5, 300, at the end.
Question: A vertical blue line in the graph. What is the equation of the line?
