Question 513662
Let:  L=Length and W=Width
Perimeter = 2L + 2W
100ft = 2(30ft) + 2W 
100ft = 60ft + 2W
100ft – 60ft  = 60ft – 60t + 2W
40ft = 2W
40ft/2 = 2W/2
20ft = W
Area = L x W
Area = 30ft x 20ft
Area = 600 sq.ft.