Hi can you answer it clearly 20. Find the volume of the largest open topped rectangular box that has a square base and a total surface area of 3600 cm^2 . 22. A cylinder of radius 'r' is inscribed in a cone of height H and base radius R. Show that the maximum volume of the cylinder is 4/9 the volume of the cone. 23. At 1 pm a Ship sailing South at 18 knots is 40 miles due East of a Boat travelling East at 24 knots. When will the two vessels be closest to each other? 24. A toy tugboat is launched from the side of a pond and travels North at 5 cm/8. At the same moment, a s toy sail ship starts from a point 82 m Northeast of the tugboat and travels West at 7 cm/8 . How s closely do the two toys approach each other? 25. Two isolated farms are situated 12 km apart on a straight country road that runs parallel to the main highway which is 20 km away. The power company decides to run a wire from the highway to a junction box, and from there, wires of equal length to the two farms. Where should the junction box be placed to minimize the length of wire needed? 26. A sailor in a rowboat that is 8 km off a straight coastline wants to reach a point on shore that is 10 km from the point directly opposite her present position. (In the shortest possible time!!) Toward what point on shore should she steer and how long does it take her to reach her destination if she can row at 4 km/h and she can run (on the beach) at 6 km/h ? 27. A real estate firm owns 250 apartments that can be rented at $460 per month each. For each $5 per month increase in rent, there are two vacancies created that cannot be filled. What should the monthly rent be to maximize the total revenue? What is the maximum revenue? 28. Electric power for a home on one bank of a straight river (that is 200 m wide) must come from a power station that is 500 m downstream on the opposite bank of the river. If it costs twice as much to lay cable underwater as it does to lay cable on land, what path should be chosen to minimize the cost of the cable