5. At a certain point on the beach, a post sticks out of the sand. The top of the post is 75 cm above the beach. The depth of the water at the post varies with time due to the tide. If h is the height of the water t hours after midnight, the equation giving the water height is h = 40 cos (30(1-3))+50. a) Sketch the graph of this function b) What is the depth of the water at 11AM? c) At what time of the day is the tide at its lowest point? d) During the first 12 hours, when is the post under water? Confirm your answer using the graph.. (10)