need help with this questions

11. The depth of water in a harbour varies as a function of time. The maximum depth is 9 feet and the minimum depth is 1 foot. The depth can be modelled with a sinusoidal function that has a period of 12 hours. If the depth is 5 feet at 12 midnight, and is increasing, a. Create an algebraic model to predict the depth of the water as a function of time. Justify your reasoning. [T4] [C2]