$$ \begin{aligned} -19-15-5f &= 7(-3f+18)&& \text{simplify left and right hand side} \\[1 em]-5f-34 &= -21f+126&& \text{move the $ \color{blue}{ -21f } $ to the left side and $ \color{blue}{ -34 }$ to the right} \\[1 em]-5f+21f &= 126+34&& \text{simplify left and right hand side} \\[1 em]16f &= 160&& \text{ divide both sides by $ 16 $ } \\[1 em]f &= \frac{160}{16}&& \\[1 em]f &= 10&& \\[1 em] \end{aligned} $$

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