Chapter 2 - Equations, Inequalities, and Problem Solving - 2.1 Solving Equations - 2.1 Exercise Set - Page 86: 31

$r=\dfrac{7}{3}$

Adding $ -\dfrac{1}{3} $ to both sides of the given equation, $ r+\dfrac{1}{3}=\dfrac{8}{3} $, then, \begin{array}{l} r+\dfrac{1}{3}-\dfrac{1}{3}=\dfrac{8}{3}-\dfrac{1}{3} \\\\ r=\dfrac{7}{3} .\end{array}