#### Answer

Answer F

#### Work Step by Step

Martin used 400 ft of fencing to enclose a rectangular area in his backyard:
$P=2(l+w)=400 \rightarrow l+w=200$
Isabella wants to enclose a similar area that is twice as long and twice as wide as the one in Martin's backyard.
$P=2(2l+2w)$
$P=4(l+w)$
$P=4 \times 200$
$P=800$ ft
The correct answer is F.