#### Answer

$\frac{\sqrt 3x}{8}$

#### Work Step by Step

$\sqrt \frac{3x^{3}}{64x^{2}}$
$x^{3} \div x^{2} $ can be simplified to x
$\sqrt \frac{3x}{64}$
We can rewrite it as
$\frac{\sqrt 3x}{\sqrt 64}$
Square root of 64 is 8 because 8 x 8 = 64
$\frac{\sqrt 3x}{8}$