Let, Length of side of square is 'a' cm In picture, Legth of 1 small sqaure =1cm
then Area of square =
If length of side is 4cm then Area of that square
If length of side is 6cm then Area of that square
Area of shaded region = Area of square with length 6 cm - Area of sqaure with length 4cm=36-16=20
So, difference between area of big sqaure and small square is 20