$$ \begin{aligned} 20d+1+10d &= 3d+1&& \text{simplify left side} \\[1 em]30d+1 &= 3d+1&& \text{move the $ \color{blue}{ 3d } $ to the left side and $ \color{blue}{ 1 }$ to the right} \\[1 em]30d-3d &= 1-1&& \text{simplify left and right hand side} \\[1 em]27d &= 0&& \text{ divide both sides by $ 27 $ } \\[1 em]d &= \frac{0}{27}&& \\[1 em]d &= 0&& \\[1 em] \end{aligned} $$

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