Factoring out a common factor of $\displaystyle{6}{{x}}^{{2}}\usepackage{cmbright}\Huge\$ , you found that $\displaystyle{18}{{x}}^{{2}}{{y}}^{{3}}-{30}{{x}}^{{3}}{{z}}^{{4}}={6}{{x}}^{{2}}{\left({3}{{y}}^{{3}}-{5}{x}{{z}}^{{4}}\right)}\usepackage{cmbright}\Huge\$ .