Question 845382
This kind of question seems so common.  What if you generally had:
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The perimeter of a rectangle is p meters .  The length is k more than the width . Set up a system of equations and solve  to find the length and width.


Let L = length
Let w = width

Perimeter information gives {{{2L+2w=p}}}.
Other description gives {{{L=k+w}}}.


Those are the equations for the system having L and w as variables, UNKNOWN variables.  Sometimes one equation or the other could use refinement or simplification before using a final form of the system of equations.  


Often the choice for which method to solve the system is the student's.  The general system shown above can easily be handled through substituting for L in the perimeter equation, and then solve for w.  ...
An alternative can be, substitute for w in one of the equations.
Another alternative is, depending on simplifications made, use the system as:
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2L+2w=p
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L-w=k
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and use Elimination Method.