Area of square painting is 400 square inches.
Let the side of square painting is = a inch
So the area of square painting is = [tex]a^2[/tex] square inch.
So [tex]a^2 = 400
a = \sqrt{400} [/tex]
[tex]a = 20 inch[/tex]
Length of wood trim to need to go around the painting is equal to the perimeter of square painting .
So the perimeter of square painting is = 4 * (side)
= 4* 20 = 80 inch.
So the required length of wood trim is = 80 inch.