You may have correctly canceled common factors, but made a mistake using the quotient rule.

$\displaystyle\frac{{{x}}^{{3}}}{{{x}}^{{9}}}={{x}}^{{{6}-{9}}}={{x}}^{{-{{3}}}}\usepackage{cmbright}\Huge\$

You can rewrite $\displaystyle{{x}}^{{-{{3}}}}\usepackage{cmbright}\Huge\$ as a fraction with a positive exponent.