$$3(2h+7) = 4\cdot(9-h)$$

$$ \begin{aligned} 3(2h+7) &= 4\cdot(9-h)&& \text{simplify left and right hand side} \\[1 em]6h+21 &= 36-4h&& \\[1 em]6h+21 &= -4h+36&& \text{move the $ \color{blue}{ -4h } $ to the left side and $ \color{blue}{ 21 }$ to the right} \\[1 em]6h+4h &= 36-21&& \text{simplify left and right hand side} \\[1 em]10h &= 15&& \text{ divide both sides by $ 10 $ } \\[1 em]h &= \frac{15}{10}&& \\[1 em]h &= \frac{3}{2}&& \\[1 em] \end{aligned} $$

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