1. The depth, D, (in metres) of water at the entrance to a harbour at t hours after midnight on a given day is represented by t D(t) = 10+ 38l11(% + g) for t e [0, 24] (a) State the amplitude, the equation of the midline, phase shift and period of D(t). (b) Sketch the graph of D(t) for t E [0, 24]. (c) Algebraically nd the intervals of time during the day when the depth is greater than 8.5 metres. ((1) A boat is permitted to enter the harbour only if the depth of water at the entrance is at least d metres for a continuous interval of three hours. Algebraically approximate the largest value of d which satises this condition