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{64}{{x}}^{{9}}-{27}{{y}}^{{6}}={{\left({4}{{x}}^{{3}}\right)}}^{{3}}-{{\left({3}{{y}}^{{2}}\right)}}^{{3}}={\left({4}{{x}}^{{3}}-{3}{{y}}^{{2}}\right)}{\left({{\left({4}{{x}}^{{3}}\right)}}^{{2}}+{4}{{x}}^{{3}}\cdot{3}{{y}}^{{2}}+{{\left({3}{{y}}^{{2}}\right)}}^{{2}}\right)}\usepackage{cmbright}\Huge\$

$\displaystyle={\left({4}{{x}}^{{3}}-{3}{{y}}^{{2}}\right)}{\left({16}{{x}}^{{6}}+{12}{{x}}^{{3}}{{y}}^{{2}}+{9}{{y}}^{{4}}\right)}\usepackage{cmbright}\Huge\$

The missing exponent is 4.