The area of a square bedroom is 144 square feet. what is the length of one wall?

The answer is:  "12 feet" .

Note:  In a square, the length of EACH of the four sides of the square is the same.

Area = Length * width. 

For a square, length = width.

So for a square, Area = length * width = (length of a side)² = s² ,

Given:  A = s² = 144 ft² ;

Solve for the positive value of "s" .

  →  s² = 144 ft² ;  Take the "square root" of each side ;

  → √(s²) = √(144 ft²) ;

  →   s = 12 ft.

The answer is:  12 ft.