Modelling Hormone Levels, from Differential Calculus from the Life Sciences (modelling with trigonometric functions)

The level of a certain hormone in the bloodstream fluctuates between undetectable concentration at t = 07:00 and 100 ng/ml (nanograms per millilitre) at t = 19:00. If the

cyclic variations in this hormone level behave in a periodic manner, what would you predict the hormone level to be at midnight?

(please explain each step for how to create a trigonometric function)