Respuesta :

tawasimialex

Answer:

the answer is D.

Step-by-step explanation:

Since the square: (3√15) is common in both of them, you only focus on 21 and 9. if you subtract 9 from 21, it will give you 12. so, just add (3√15) to 12, which will give you: 12^3sqrt15

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