Find the volume in the first octant bounded by the surfaces,

$\displaystyle 4x+4y+z = 16, z=0, y=\frac{x}{2},y=2x$

See figure attached for my attempt.

Not sure where I went wrong on this one, I think I got a good sketch of the actual volume, it looks like very thin slice of cheese of some sort.

Is the mistake in the way I set up my integral? Or in evaluating the integral itself? Or both?

Thanks again!