you must build a 3 sided pen along a river bank that flows horizontally through a plot of land. The exterior fencing for three sides cost $10 per foot. the pen must also have three interior vertical dividers, that cost 6$ per foot. (note each of the four interior sections will have access to the river) if you have $36,000 to spend, what dimensions for the fencing will maximize the total bounded area? What is the maximum area?