Addition and Subtraction of Radicals

$\rhd$ Simplifying radical expressions (addition) (4:40) Simplify $\sqrt{2x^2} + 4\sqrt{8} + 3\sqrt{2x^2} + \sqrt{8}$ .
$\rhd$ Simplifying radical expressions (subtraction) (5:46) Simplify $4\sqrt[4]{81x^4}-2\sqrt[4]{81x^5} - \sqrt{x^3}$ .