This is a problem in my book and I don't know how it came to the answer.

A rancher has 200 feet of fencing to enclose two adjacent rectangular corrals.

y[______|______] basically how the figure looks

<--x--> <--x-->

It says to write the area A of the corral as a function of x.

The answer is A=8x(50-x) / 3

I'm confused.