#### Answer

$a)$ $x\sqrt{x}$
$b)$ $x\sqrt[5]{x}$

#### Work Step by Step

$a)$ $\sqrt{x^{3}}$
Rewrite $x^{3}$ as $x^{2}\cdot x$ and then simplify:
$\sqrt{x^{3}}=\sqrt{x^{2}\cdot x}=x\sqrt{x}$
$b)$ $\sqrt[5]{x^{6}}$
Rewrite $x^{6}$ as $x^{5}\cdot x$ and simplify:
$\sqrt[5]{x^{6}}=\sqrt[5]{x^{5}\cdot x}=x\sqrt[5]{x}$