$$3(3x-7)+7 = 4\cdot(5-2x)$$

$$ \begin{aligned} 3(3x-7)+7 &= 4\cdot(5-2x)&& \text{simplify left and right hand side} \\[1 em]9x-21+7 &= 20-8x&& \\[1 em]9x-14 &= -8x+20&& \text{move the $ \color{blue}{ -8x } $ to the left side and $ \color{blue}{ -14 }$ to the right} \\[1 em]9x+8x &= 20+14&& \text{simplify left and right hand side} \\[1 em]17x &= 34&& \text{ divide both sides by $ 17 $ } \\[1 em]x &= \frac{34}{17}&& \\[1 em]x &= 2&& \\[1 em] \end{aligned} $$

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