12 inches.
The other person who answered is wrong. He or she took it as perimeter.
Why 12 inches?
Because of
1) Square have equal sides
2) This is AREA not perimeter.
So to get 144 square inches, apply the formula for area of square...
Area of square = Length times Length
So 12 times 12, you will get 144.
Or simply use surd on calculator lol.