Captain Highliner needs your help (again!). The Captain is currently fishing on the planet Rigel VI where the tides have a period of 18 hours! The Captain's ship is currently in a harbour and the depth of water at the entrance to the harbour varies from a low of 1.5 metres at low tide to 17.5 metres at high tide. The Captain's ship requires 4 metres of water to operate. The tide is currently at its lowest point. a) Create a sinusoidal function to model the depth of water over time at the entrance to the harbour. (2) b) What is the earliest time that the ship could leave the harbour? (2) c) What is the latest time that the ship could return to harbour? (2)