| $$ \begin{aligned}6x+4x+3x+2x& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}15x\end{aligned} $$ | |
| ① | Combine like terms: $$ \color{blue}{6x} + \color{red}{4x} + \color{green}{3x} + \color{green}{2x} = \color{green}{15x} $$ |