So we want to know what is the area of the shaded reagion that consists of a circle inside a square If the side of the square is a=10cm. For that we simply calculate both areas and subtract the area of a circle from the area of a square: area of a square A=10^2=100 cm^2, area of a circle B=pi*r^2 where r=a/2. So: B=3.14*5^2=78.5cm^2: A-B=100-78.5=21.5cm^2 So the correct answer is D