Question 877900
l looks like 1.  Too hard to read.  Use a better variable, maybe <b>L</b>.


Your description is transcribable as L=24+w and 2w+2L=84, from which the system easily formed can be:

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{{{highlight_green(w-L=-24)}}}
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{{{highlight_green(w+L=42)}}}
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Elimination Method is the best choice to solve the system.