8. The water depth in a harbour is 8 m at low tide and 20 metres at high tide. One cycle is completed approximately every 12 hours. Assume that the relationship between water depth, d(t), in metes, and the time, t, in minutes, is sinusoidal. Determine the hour(s) when the water depth is 16 m, to the nearest hundredth of an hour, during the first cycle.

Assume at time zero, the water level is at high tide.

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