What is the greatest area of a pasture in the shape of a rectanhle that can be fenced with 6000FT of fencing?

What is the greatest area of a pasture in the shape of a rectanhle that can be fenced with 6000FT of fencing? Can someone help me solve this with an explaination? I'm having some trouble with it. Must have something to do with the vertex of the parbola right?|||6000/4 (sides of the rectangle) = 1500 = 1500^2 (LxW)=2250000sq'