I think I have this one right but I'm not sure. Here's what I have

The problem states: A farmer plans to fence in a rectangular pasture containing three adjacent pens of equal size, lined up end-to-end. The total length of fencing needed to enclose the three pens is 1200 yards. Find the maximum total area that all three pens can enclose.

So I set up the equation as follows

Apply Quotient Rule

so

What did I do wrong?

Thanks