$$ \begin{aligned} \frac{4}{5}y+y &= 18&& \text{multiply ALL terms by } \color{blue}{ 5 }. \\[1 em]5 \cdot \frac{4}{5}y+5y &= 5\cdot18&& \text{cancel out the denominators} \\[1 em]4y+5y &= 90&& \text{simplify left side} \\[1 em]9y &= 90&& \text{ divide both sides by $ 9 $ } \\[1 em]y &= \frac{90}{9}&& \\[1 em]y &= 10&& \\[1 em] \end{aligned} $$

This page was created using