Set the following: Length = L Width = W
The length is twice the width: L = 2*W or: W = L/2
Perimeter: P = 60ft = 2*L + 2*W
Substituting L for W in the perimeter equation gives:
P = 60ft = 2*L + 2*(L/2) = 2*L + L = 3L
L = 60ft/3 = 20ft W=L/2=20ft/2=10ft
Verify result: Perimeter= P = 60ft = 2L + 2W = 2*20ft +2*10ft = 40ft+20ft = 60ft
The area of the rectangular is: Area = A = Length*Width = L*W = 20ft*10ft = 200 (ft)^2
-Rosie