First, I would find the radius for both discs. To do so, divide the circumference by 2. So.. 27.3/2=13.65. 22.5/2=11.25. Afterwards, take the radius and use the formula: 2(3.14)r. 2*3.14*13.65＝85.722 and 2*3.14*11.25＝70.65. Then, you subtract 85.722 from 70.65 which equals 15.072 which rounds to 15.
