It should be the circumference of a big circle plus the circumference of two small circles. The formula of the circumference of a circle is 2π r, specifically, the radius of the first small circle is 4/2=2, and the circumference is 2xπx2=4π. The radius of the second small circle is 6/2=3, and the circumference is 2xπx3=6π. The third is a big circle: 2xπx(2+3)= 10π. So the total circumference is: 4π+6π+ 10π=20π. I hope I can help you.