$$ \begin{aligned} 2x+7x+5 &= -x+75&& \text{simplify left side} \\[1 em]9x+5 &= -x+75&& \text{move the $ \color{blue}{ -x } $ to the left side and $ \color{blue}{ 5 }$ to the right} \\[1 em]9x+x &= 75-5&& \text{simplify left and right hand side} \\[1 em]10x &= 70&& \text{ divide both sides by $ 10 $ } \\[1 em]x &= \frac{70}{10}&& \\[1 em]x &= 7&& \\[1 em] \end{aligned} $$

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