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]