Question 1075802
Length is  {{{sqrt(12^2-x^2)}}} from Pythagorean Theorem formula.



If L is length,
{{{2L+2x=28}}}
{{{L+x=14}}}
{{{L=14-x}}}
Find L^2.
{{{L^2=14^2-28x+x^2}}}

.

{{{L^2=144-x^2}}}


Equate the two expressions of L^2.
{{{x^2-28x+196=-x^2+144}}}

{{{2x^2-28x+196-144=0}}}

{{{x^2-14x+26=0}}}

you can finish from here.