The depth of the water at the end of a pier changes periodically along with the movement of tides. on a particular day, low tides occur at 12: 00 am and 12: 30 pm, with a depth of 2.5 m, while high tides occur at 6: 15 am and 6: 45 pm, with a depth of 5.5 m. let t = 0 be 12: 00 am.