Help with 4,5,6. Please show full solutions, will like answer and give feedback!

4. (3 marks) A rectangle has its base on the x-axis and its upper vertices on the parabola y = 9-x2. Find the maximum possible area of the rectangle. 5. (3 marks) The following is the sketch of the graph of f'(x). Use this graph to find the increas ing/decreasing intervals of f, points on x-axis at which f has a local max/min and inflection points and the intervals on which f is concave up/down. 6. (3 marks) The cost of laying a fibre optic cable underwater is 3 times that of underground. An island is 4 km from point S on the shore and a broadcast station, B, is 14 km along the shore, perpendicular to S. How should the cable be laid to keep cost to a minimum