if the width = w and length = l we have
lw = 20 (area)
and 2l + 2w = 18 (perimeter)
which is same as l + w = 9
from first equation w = 20/ l so substituting in l + w = 9:-
20/ l + l = 9
20 + l^2 = 9l
l^2 - 9l + 20 =
(l - 5)(l - 4) = 0
so l is 5 or 4
But it must be 5 because length must be greater than width
So answer is length = 5 feet
