Question 891019
"border around" is perimeter.


w for width
L for length

{{{wL=40}}} and {{{2w+2L=26}}}
Some simplification and then substitution:
{{{w+L=13}}}
{{{L=13-w}}}

-
{{{w(13-w)=40}}}
{{{-w^2+13w=40}}}
{{{w^2-13w=-40}}}
{{{w^2-13w+40=0}}}
Discriminant is {{{169-4*40=169-160=highlight_green(9)}}}
{{{w=(13+- 3)/2}}}
{{{w=8}}} or {{{w=5}}}


In this case, either dimension is 5 and the other dimension is 8.