C because first you would find the circumference of the circle which is pi times diameter, which is 18.84 but since it is a semi-circle you would divide by 2 which is 9.42. Then you do 3+3=6 + the length which is 6 so you get 12. 12+9.42=21.42 and if you round that to the nearest tenth it is 21.42.
