$$6 \sqrt{ 7 \sqrt{ 9 \div 2 \sqrt{ x } } } xxxxxxx$$
$3\sqrt{21}\times 2^{\frac{3}{4}}x^{\frac{57}{8}}$
$\frac{171\sqrt{21}\times 2^{\frac{3}{4}}x^{\frac{49}{8}}}{8}$
