A three-sided fence is to be built next to a straight

Last updated: 8/11/2022

A three-sided fence is to be built next to a straight section of the Aterno-Pescara river, which forms the fourth side of a rectangular region, as shown in the diagram. The enclosed area is to equal 1800 m² and the fence running parallel to the river must be set back at least 20 m from the river. Determine the minimum perimeter of such an enclosure and the dimensions of the corresponding enclosure.