Question 337779
It's not possible.
The most efficient shape is the square that provides the maximum area for a given perimeter.
For a perimeter of 24 ft, the side of the square, {{{s}}} would be,
{{{s=P/4=24/4=6}}}
The maximum area that can be developed with 24 feet of fencing would be, 
{{{A=s^2=36}}} sq. ft.
Consider using the wall of a building to reduce the need for fencing on one or more sides.