## Elementary Algebra

$n=14$
Using cross-multiplication and the properties of equality, the value of the variable that satisfies the given equation, $\dfrac{n}{20-n}=\dfrac{7}{3} ,$ is \begin{array}{l}\require{cancel} 3(n)=7(20-n) \\\\ 3n=140-7n \\\\ 3n+7n=140 \\\\ 10n=140 \\\\ n=\dfrac{140}{10} \\\\ n=14 \end{array}