Answer:
1. The amplitude of the function is 12 feet, since it moves from 6 feet above to 6 feet below the average sea level.
2. The period of the function is 12 hours, since it takes 12 hours for the tide to go from high to low and back again.
3. The frequency of the function is 0.5 (1/12), since it takes 12 hours for the function to repeat itself.
4. The midline of the function is the average sea level.
5. There is no vertical shift.
6. The phase shift is 0, since the first high tide occurs at x = 0.