Question 547673
Area = 40
perimeter =26

L*W=40
L=40/w

Perimeter = 2(L+W)=26

substitute L 

2(40/w  + w)=26
2(40+w^2)/W=26
40+W^2=26*w/2
W^2+40=13W
W^2-13W+40=0
W^2-8W-5W+40=0
W(W-8)-5(W-8)=0
(W-8)(W+5)=0
so W=8m the positive value

length = 5 m