area=legnth times width
width=2/3 legnth
w=2/3l
a=lw
subsitute
a=l(2/3l)
a=864
864=2/3l^2
multiply both sides by 3/2 to clear fraction
2592/2=l^2
1296=l^2
square root both sides
36=legnth
width=2/3 legnth
width=2/3 times 36
width=72/3=24
legnth =36 feet
width=24 feet