Chapter 2 - Equations, Inequalities, and Problem Solving - 2.1 Solving Equations - 2.1 Exercise Set - Page 87: 57

$x=20$

Multiplying both sides by $ \dfrac{5}{4} $, then the solution to the given equation, $ \dfrac{4}{5}x=16 $, is \begin{array}{l}\require{cancel} \dfrac{5}{4}\cdot\dfrac{4}{5}x=16\cdot\dfrac{5}{4} \\\\ \dfrac{\cancel{5}}{\cancel{4}}\cdot\dfrac{\cancel{4}}{\cancel{5}}x=\dfrac{80}{4} \\\\ x=20 .\end{array}