How do you know the shaded circle are 3/4 of the entire circle on page 271 question 4
![](https://i0.wp.com/pwntestprep.com/wp-content/uploads/2020/08/image-6.png?resize=331%2C196&ssl=1)
Angles A and C are 90° angles (the question tells you ABCD is a square) and we know A and C are the centers of their respective circles (the question tells you that, too).
90° is 1/4 of 360°, so each circle is missing 1/4 of itself.