Question

Given ƒ(x) = 3x + 9, find x when ƒ(x) = 21.

A) 3
B) 4
C) 7
D) 10

Answer 1

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

Answer 2

B

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.