Why are the areas of unshaded regions in the two figures equal?
Both A and B
The two areas are equal because the four quarter circles in the first figure has the same radius as the circle. The area of shaded region in the first figure is the area of the square without the four quarter circles (marked as 1,2,3 and 4), and the area of the shaded region in the second figure is the area of the square without the circle. Also, the radii of the quarter circles 1,2,3 and 4 are equal.