Question 339134
Where are your variables?
{{{L}}}-length
{{{W}}}-width
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{{{L=W+18}}}
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The area of a rectangle is,
{{{A=L*W=88}}}
Now substitute for {{{L}}} in the area equation. 
{{{(W+18)*W=88}}}
{{{W^2+18W=88}}}
{{{W^2+18W-88=0}}}
You can factor this quadratic equation. 
Then only use the positive solutions for {{{W}}} since {{{W}}} can't be negative.
Once you have {{{W}}} solve for {{{L}}} with the equation from above.