let l be the length and w be the width.
so 2l + 2w =36
also, l = 2w,
Putting the value for l in the first equation:
2(2w) + 2w = 36
4w + 2w = 26
6w = 36
w = 6
now solving for the length:
l = 2w
l = 2(6)
so the length will be 12, l = 12
So the width is 6. the length is 12.
and the area is lxw, so the area will be 72