$$ \begin{aligned} 21 &= \frac{1}{6}x+20&& \text{multiply ALL terms by } \color{blue}{ 6 }. \\[1 em]6\cdot21 &= 6 \cdot \frac{1}{6}x+6\cdot20&& \text{cancel out the denominators} \\[1 em]126 &= x+120&& \text{ swap the left and right side of the equation } \\[1 em]x+120 &= 126&& \text{ move 120 to the right } \\[1 em]x &= 126-120&& \\[1 em]x &= 6&& \\[1 em]x &= 6&& \\[1 em] \end{aligned} $$

This page was created using