Answer
$10x\sqrt{5x}$
Work Step by Step
Using the properties of radicals, then,
\begin{array}{l}
3\sqrt{45x^3}+x\sqrt{5x}
\\=
3\sqrt{9x^2\cdot5x}+x\sqrt{5x}
\\=
3\cdot3x\sqrt{5x}+x\sqrt{5x}
\\=
9x\sqrt{5x}+x\sqrt{5x}
\\=
10x\sqrt{5x}
.\end{array}