#### Answer

$2x\sqrt {3x}$

#### Work Step by Step

$x\sqrt {75x}-\sqrt {27x^{3}}$
=$x\sqrt {25\times3\times x}-\sqrt {9\times3\times x \times x^{2}}$
=$x\sqrt {5^{2}\times3\times x}-\sqrt {3^{2}\times3\times x \times x^{2}}$
=$5x\sqrt {3x}-3x\sqrt {3x}$
=$(5x-3x)\sqrt {3x}$
=$2x\sqrt {3x}$