I have to practice Ocean tides, oscillating springs, and ferris wheel problems for a test tomorrow

Desired result is a full example of one of the problems, or a link to a website that has examples, im also concerned about getting good communication marks so i need to know how to do it properly on this question. one full example on how to solve this question so i can use it as a model to solve others would be optimal please and thank you

Sample question:

The water depth in a harbour is 21 m at high tide ad 11 m at low tide. One cycle is completed aproximaately every 12 h.

a) find the equation for the water depth as a function of time , t hours , after low tide

b) draw a graph of the function for the 48 h after low tide which occurred at 14:00

d) find the depth of the water at

i)17:45

ii) 21:00

i would like full answers to the quiestions above if possible because time is of the essence

i amnotasking you to do my homework i just need an exaample, as you can see that is 1/2 of that question and i still need to practice other 3 situations.. i only put up essential part of the question

PLease(Bow) Ty