A rancher wants to construct three identical rectangular corrals using 2400 feet of fencing. The rancher decides to build them adjacent to each other, so they share fencing on one or both sides. What dimensions should the rancher use to construct each corral so they will enclose the largest possible area?

This is about Applications of Derivatives

this is what I have so far

2400 ft = 2x + 4y

A = xy

Thank you!