Answer: [tex]9\ units[/tex]
Step-by-step explanation:
You need to use the following formula for calculate the area of a square:
[tex]A=s^2[/tex]
Where "s" is the lenght of any side of the square.
You know that the area of a mural is [tex]81\ units^2[/tex]. Then, you can substitute this area into the formula and solve for "s", in order to find the side lenght of the mural.
Therefore, this is:
[tex]81\ units^2=s^2\\\\s=\sqrt{(81\ units^2)}\\\\s=9\ units[/tex]