Question 523386
P = perimeter
P = 54 in.
P = 2(L+W), where L=Length and W=Width
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L = W+3
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substitute
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2(W+3) + 2W = 54
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2W +6 +2W = 54
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4W = 48
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W = 12
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L = W+3
L = 12+3
L = 15
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Check the perimeter to be sure this solution is the answer.
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2L = 2(15) = 30
2W = 2(12) = 24
30+24 = 54
Correct.
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Answer: Length = 15 inches; Width = 12 inches.
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Is this a deck for a doll house?  Just wondering...(smile)