Shaded Area: Star in the Square

Explanations

1. The four non-shaded parts can be rearranged to create a full circle with the radius of r = 8/2 = 4.
2. The area of the obtained circle: pi*r^2 = 3.14*4^2 = 50.24.
3. The area of the square: 8*8 = 64.
4. The area of the shaded part is a difference between (3) and (2): 64 - 50.24 = 13.76.