width = 82 feet, length = 123 feet
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First, write down equations that express what you've been given.
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w = 2/3 l
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p = 410
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p = 2(w+l)
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Since we have an expression that defines w in terms of l, substitute for w, the expression. Also substitute the known value for p in the expression.
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p = 2(w + l)
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410 = 2( 2/3 l + l)
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Combine the l terms
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410 = 2( 5/3 l)
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Multiply
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410 = 10/3 l
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Multiple both sides by 3
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1230 = 10 l
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Divide both sides by 10
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123 = l
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So we now know the length is 123 feet.
So plug in the known value of l into the formula w = 2/3 l to get the width
w = 2/3 123 = 82