| $$ \begin{aligned}3(x+9)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}3x+27\end{aligned} $$ | |
| ① | Multiply $ \color{blue}{3} $ by $ \left( x+9\right) $ $$ \color{blue}{3} \cdot \left( x+9\right) = 3x+27 $$ |