Below is the graph of a trigonometric function. It has a maximum point at $(1.2,5.5)$ and an amplitude of 3.5 . What is the midline equation of the function?

Please directly answer the question and provide the final value, e.g., 1, 2.5, 300.
Question: Below is the graph of a trigonometric function. It has a maximum point at $(1.2,5.5)$ and an amplitude of 3.5 . What is the midline equation of the function?

Please first conduct reasoning, and then answer the question and provide the final value, e.g., 1, 2.5, 300, at the end.
Question: Below is the graph of a trigonometric function. It has a maximum point at $(1.2,5.5)$ and an amplitude of 3.5 . What is the midline equation of the function?
