Ok so if The area of the square is 15 * 15. then what you need to do is subtract the total area of the 4 white sectors of a circle. Together, the 4 sectors form one circle of radius 7.5. Now yu need to have in mind that the area of the circle they jointly form is pi * (7.5)^2. So 15 * 15 - pi * (7.5)^2 =48.29
Hope this is useful