Capybara Corral

Farmer Mead has 48 meters of fence in her barn. She wants to make a rectangular pen to hold as many capybaras as possible, allowing one square meter of space for each animal.

During the night she had an idea. Could she make a larger pen by using one side of the barn as a side of the pen? Then the 48 meters of fence only have to go around three sides.

Find out how she should build the pen to allow maximum area.