Respuesta :
Answer:
All real numbers
Step-by-step explanation:
21 - 7x = 7(3 - x)
21 - 7x = 21 - 7x
Since both sides of the equation are equal, the answer is all real numbers.
[tex]21 - 7x = 7(3 - x)\\21 - 7x = 21 - 7x\\-7x + 7x = 21 - 21\\x \in \mathbb{R}[/tex]