Correct. A binomial in the form $\displaystyle{{a}}^{{3}}-{{b}}^{{3}}\usepackage{cmbright}\Huge\$ can be factored as $\displaystyle{\left({a}-{b}\right)}{\left({{a}}^{{2}}+{a}{b}+{{b}}^{{2}}\right)}\usepackage{cmbright}\Huge\$ .

$\displaystyle{{x}}^{{6}}-{27}{{y}}^{{9}}={{\left({{x}}^{{2}}\right)}}^{{3}}-{{\left({3}{{y}}^{{3}}\right)}}^{{3}}={\left({{x}}^{{2}}-{3}{{y}}^{{3}}\right)}{\left({{\left({{x}}^{{2}}\right)}}^{{2}}+{{x}}^{{2}}\cdot{3}{{y}}^{{3}}+{{\left({3}{{y}}^{{3}}\right)}}^{{2}}\right)}\usepackage{cmbright}\Huge\$

$\displaystyle={\left({{x}}^{{2}}-{3}{{y}}^{{3}}\right)}{\left({{x}}^{{4}}+{3}{{x}}^{{2}}{{y}}^{{3}}+{9}{{y}}^{{6}}\right)}\usepackage{cmbright}\Huge\$

The missing exponent is 3.