Final answer:
The given multi-step equation is solved by distributing, combining like terms, and isolating x to find that x = 13. However, this does not match any of the answer choices, suggesting a possible error in the question's information.
Step-by-step explanation:
To solve the multi-step equation 3x + 2(4 - x) = 21 and find the value of x that equals 9, we need to combine like terms and simplify.
- First, distribute the 2 into the parentheses: 3x + 8 - 2x = 21.
- Combine like terms by subtracting 2x from 3x: x + 8 = 21.
- Subtract 8 from both sides to isolate x: x = 21 - 8.
- Simplify to find the value of x: x = 13.
However, since none of the answer choices match this result, and the goal is to find a solution where x equals 9, there might be a misunderstanding in the equation provided or the expected result. Be sure to check the initial equation and the values provided carefully.