$$ \begin{aligned} 6j-3 &= 7j+6&& \text{move the $ \color{blue}{ 7j } $ to the left side and $ \color{blue}{ -3 }$ to the right} \\[1 em]6j-7j &= 6+3&& \text{simplify left and right hand side} \\[1 em]-j &= 9&& \text{switch signs on both sides} \\[1 em]j &= -9&& \\[1 em] \end{aligned} $$