So I am having some trouble with a certian type of question that has arisen in some of the past work I have done leading me to believe that it could appear in my upcoming examination. So on with the question:

A farmer plans to use a river as a one boundary of a rectangular paddock. If the farmer has 480m of fencing to be used to fence the remaining 3 sides, what dimensions should the paddock be to ensure maximum area.

Help is greatly appriciated.