$$ \begin{aligned} 7x+7 &= -1+6x&& \text{move the $ \color{blue}{ 6x } $ to the left side and $ \color{blue}{ 7 }$ to the right} \\[1 em]7x-6x &= -1-7&& \text{simplify left and right hand side} \\[1 em]x &= -8&& \\[1 em]x &= -8&& \\[1 em] \end{aligned} $$