The first one is C = 2 pi r or C = pi * d
d = 8.4
C = 8.4* pi
D answer <<<<<<
The second one I got the same answer you did.
Just to confirm
C = 2 pi r
C = 2 pi r / 4 to get 1/4 of the circumference.
C = 1/2 pi r
Now you take that away from the entire circle
C_3/4 = 2 pi r -1/2 pi r
C_3/4 = 3/2 pi r Since r is 6 put it in for r
C_3/4 = 3/2 pi * 6
C_3/4 = 9 pi
Note you may not have done it the same way. No matter.
B <<<< answer