It's called perfect cubes

For the statement to be true, 'a' and 'b' must be equal
*First expand the binomial using FOIL, then set it equal to whats given "2abi".
Then you can find the relationship between a and b.
If it bisect, then using the Line Bisector Theorem, it must be equal.
So x+6=4x-21
get like terms on 1 side
x+6=4x-21
-x. +21
27= 3x
x=9
plug the x in
CD= 9+6
CD=15
Option A
Must click thanks and mark brainliest
Sorry if i am wrong
Answer:
31
Step-by-step explanation: