W=4L/9
A=LW, using W found above gives us
A=L(4L/9)
A=4L^2/9 and we were told that A=576 so
4L^2/9=576 multiply both sides by 9
4L^2=5184 divide both sides by 4
L^2=1296 take the square root of both sides
L=36, and we know that W=4L/9 so
W=4(36/9)=16
So the dimensions are: width=16in and length=36in