first, the bigger square's area is 20*20= 400 cm^2
second, the circle's area is ¶r^2 = ¶(20/2)^2 = ¶(10)^2 = 100¶ cm^2
third, smaller square-- if we imagine it as 4 parts as 4 right triangles-- 1 part will be 1/2*(20/2)(20/2) = 1/2 (10)(10) = 50 cm^2 then the area of the smaller square is 4*50 = 200 cm^2
so the shaded parts = circle - smaller square =100¶ - 200 cm^2
the answer is 2