Just an answer and simple explanation! Thank you.
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Answer:
15
Step-by-step explanation:
If CD and DE equal, then x+6 = 4x -21
So if you subtract x from both sides and plus 21 to both sides, that would be 3x = 27. Divide by 3 on both sides and you get 9.
Plug in x+6 with 9 and you get 15.