Question 884191
Let w = width
Let L = Length


The description's first sentence you can transcribe into {{{w=-10+L/2}}}.
The second sentence giving perimeter can be set into the formula for the perimeter of a rectangle, {{{2w+2L=52}}}.  Sometimes, drawing an rectangle and labeling the parts with the corresponding symbols can help.


Both of those equations use variables L and w.  You have a formula for w already, and so you can substitute that expression into the other equation.


{{{2w+2L=52}}}
{{{2(-10+L/2)+2L=52}}}
{{{L-20+2L=52}}}
{{{3L-20=52}}}
{{{3L=52+20}}}
{{{3L=72}}}, now divide both sides by 3,
{{{L=24}}}


Now use that to get the value for w.