Chapter 7 - Section 7.4 - Adding, Subtracting, and Multiplying Radical Expressions - Exercise Set - Page 439: 37

$\dfrac{5x\sqrt[3]{x}}{7}$

Using the properties of radicals, then, \begin{array}{l} \dfrac{\sqrt[3]{8x^4}}{7}+\dfrac{3x\sqrt[3]{x}}{7} \\\\= \dfrac{\sqrt[3]{8x^3\cdot x}}{7}+\dfrac{3x\sqrt[3]{x}}{7} \\\\= \dfrac{2x\sqrt[3]{x}}{7}+\dfrac{3x\sqrt[3]{x}}{7} \\\\= \dfrac{5x\sqrt[3]{x}}{7} .\end{array}