Solve the following.

a. A rectangular pen is built with one side against a barn. If 2100 m of fencing are used for the other three sides of the pen, what dimensions maximize the area of the pen? b. A rancher plans to make four identical and adjacent rectangular pens against a barn, each with an area of 100 m Barn (see figure). What are the dimensions of each pen that minimize the amount of fence that must be used? 100 100 100 100