Chapter 7 - Section 7.4 - Adding, Subtracting, and Multiplying Radical Expressions - Exercise Set - Page 438: 14

$\dfrac{3\sqrt[3]{4}}{14}$

Using the properties of radicals, then, \begin{array}{l} \dfrac{2\sqrt[3]{4}}{7}-\dfrac{\sqrt[3]{4}}{14} \\\\= \dfrac{2(2\sqrt[3]{4})-\sqrt[3]{4}}{14} \\\\= \dfrac{4\sqrt[3]{4}-\sqrt[3]{4}}{14} \\\\= \dfrac{3\sqrt[3]{4}}{14} .\end{array}