Question 863731
Uncut square, {{{x^2}}} area.  Side length is x.


Remaining rectangle, {{{x(x-3)}}} area.  This was given a value {{{10*cm^2}}}.
{{{x^2-3x=10}}}
{{{x^2-3x-10=0}}}
{{{(x+2)(x-5)=0}}}


The meaningful solution is {{{highlight(x=5)}}}.