Question 936538
Let x be the side of the square.
{{{x^2=A}}} and A is not given but expected to be a constant.


The dimensions of the rectangle:  {{{x+8}}} and {{{x-4}}}.


Same areas, so {{{(x+8)(x-4)=A}}}.


The situation is of two expressions for the same area A.


{{{highlight_green((x+8)(x-4)=x^2)}}}
You do the rest.  Any difficulty?
(Could be solved in three steps, maybe four).




x=8