$$ \begin{aligned} 3\cdot(2+5x)-4 &= 7-2\cdot(3-x)&& \text{simplify left and right hand side} \\[1 em]6+15x-4 &= 7-(6-2x)&& \\[1 em]15x+2 &= 7-6+2x&& \\[1 em]15x+2 &= 2x+1&& \text{move the $ \color{blue}{ 2x } $ to the left side and $ \color{blue}{ 2 }$ to the right} \\[1 em]15x-2x &= 1-2&& \text{simplify left and right hand side} \\[1 em]13x &= -1&& \text{ divide both sides by $ 13 $ } \\[1 em]x &= -\frac{1}{13}&& \\[1 em] \end{aligned} $$

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