Respuesta :

rsunil0001

Answer:

B

Step-by-step explanation:

Replacing f(x) with 21, this is the equation

21=3x+9

First, subtract 9 from each side of the equation to get:

12 = 3x

Next, divide each side by 3 to get:

4 = x

So the answer is B.

jessbean55
x=21
21-9=12
3x=12
12divided by 3=4
X=4. The answer is B