$$ \begin{aligned} 3(b-3) &= 4(b-5)&& \text{simplify left and right hand side} \\[1 em]3b-9 &= 4b-20&& \text{move the $ \color{blue}{ 4b } $ to the left side and $ \color{blue}{ -9 }$ to the right} \\[1 em]3b-4b &= -20+9&& \text{simplify left and right hand side} \\[1 em]-b &= -11&& \text{switch signs on both sides} \\[1 em]b &= 11&& \\[1 em] \end{aligned} $$

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