#### Answer

$9x\sqrt{3x}$

#### Work Step by Step

$5\sqrt{27x^3}-3x\sqrt{12x}$
Factor out perfect squares.
$5\sqrt{(9)(3)(x^2)(x)}-3x\sqrt{(4)(3)(x)}$
Simplify.
$(5)(3)(x)\sqrt{3x}-(3x)(2)\sqrt{3x}$
$15x\sqrt{3x}-6x\sqrt{3x}$
Subtract like radicals.
$9x\sqrt{3x}$