This is my question:

Antonio wants to build a rectangular pen for his animals. One side of the pen will be against the barn; the other three sides will be enclosed with wire fencing. If Antonio has 550 feet of fencing, what dimensions would maximize the area of the pen?

a) Letbe the length of the pen perpendicular to the barn. I need an equation to model the area of the pen in terms ofw.

Area =

What widthwould maximize the area?

w=

don't understand how to handle a problem like this?