4. 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 + hours after midnight, the equation giving the water height is h = 50+ 40 cos " (t - 3). 6 a) Sketch the graph of this function. b) What is the depth of the water at 11 am? c) At what time of the day is the tide at its lowest? 5. The percentage of carbon dioxide in the atmosphere varies over the course of the year, as follows: Day of the year 0 61 121 183 244 300 365 426 % of Carbon dioxide 20 19.7 18.2 17 17.9 19.6 20 19.6 a) Draw a graph of the graph. b) Find an equation of the curve. c) Why do you think the amount of CO, varies this way