Fence dimensions calculus help

[jenc305]

A rectangular study area is to be enclosed by a fence and divided into two equal parts, with a fence running along the division parallel to one of the sides. If the total area is 384 ft^2, find the dimensions of the study area that will minimize the total length of the fence. How much fence will be required?

This is what I have so far:
P=3y+4x
y=384ft^2/x
P=3(384ft^2)/x+4x
P=1152ft^2/x+4x

I'm not sure what to do next.

Thanks for the help!

 

[Galileo]

How did you get P=3y+4x?
Don't you have P=3x+2y? (Twice the length, twice the width and one division equal to either x or y?)

You have to minimize P, so try differentiating it to find the extrema.