Respuesta :

Answer: C

Step-by-step explanation:

21x+9-3x = 18x + 9

If you factor out the 9, you would be left with

9 (2x+1)

Answer: A. 9(2x - 1)

Step-by-step explanation:

combine like terms

21x+9-3x

21x-3x

18x+9

Factor the expression

factor out 9 from the expression

you get 9(2x - 1)