$$3x\cdot7+2x+1-(x\cdot2+x-1) = 0$$

$$ \begin{aligned} 3x\cdot7+2x+1-(x\cdot2+x-1) &= 0&& \text{simplify left side} \\[1 em]21x+2x+1-(3x-1) &= 0&& \\[1 em]23x+1-(3x-1) &= 0&& \\[1 em]23x+1-3x+1 &= 0&& \\[1 em]20x+2 &= 0&& \text{ move the constants to the right } \\[1 em]20x &= -2&& \text{ divide both sides by $ 20 $ } \\[1 em]x &= -\frac{2}{20}&& \\[1 em]x &= -\frac{1}{10}&& \\[1 em] \end{aligned} $$

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