$$ \begin{aligned} 2(7f+4)-4f &= 8f&& \text{simplify left side} \\[1 em]14f+8-4f &= 8f&& \\[1 em]10f+8 &= 8f&& \text{move the $ \color{blue}{ 8f } $ to the left side and $ \color{blue}{ 8 }$ to the right} \\[1 em]10f-8f &= -8&& \text{simplify left side} \\[1 em]2f &= -8&& \text{ divide both sides by $ 2 $ } \\[1 em]f &= -\frac{8}{2}&& \\[1 em]f &= -4&& \\[1 em] \end{aligned} $$

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