$$ \begin{aligned} 5x-9 &= 6x-3&& \text{move the $ \color{blue}{ 6x } $ to the left side and $ \color{blue}{ -9 }$ to the right} \\[1 em]5x-6x &= -3+9&& \text{simplify left and right hand side} \\[1 em]-x &= 6&& \text{switch signs on both sides} \\[1 em]x &= -6&& \\[1 em] \end{aligned} $$