Позбування числа пiд x

$$\begin{array}{llll}\hfill \frac{x}{3}-4& =3& \hfill & \\ \hfill \frac{x}{3}& =3+4& \hfill & \\ \hfill \frac{x}{3}& =7& \hfill & \\ \hfill 3\times \frac{x}{3}& =7\times 3& \hfill & \\ \hfill \text{<mn>3</mn>}\times \frac{x}{\text{<mn>3</mn>}}& =7\times 3& \hfill & \\ \hfill x& =21& \hfill & \end{array}$$