Question
$$1+\frac{r}{9} = 4$$
Answer
$$ r = 27 $$
Explanation
$$ \begin{aligned} 1+\frac{r}{9} &= 4&& \text{multiply ALL terms by } \color{blue}{ 9 }. \\[1 em]9\cdot1+9 \cdot \frac{r}{9} &= 9\cdot4&& \text{cancel out the denominators} \\[1 em]9+r &= 36&& \text{ move 9 to the right } \\[1 em]r &= 36-9&& \\[1 em]r &= 27&& \\[1 em]r &= 27&& \\[1 em] \end{aligned} $$
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