The GCF of the three terms is $\displaystyle{3}{x}\usepackage{cmbright}\Huge\$ , so $\displaystyle{3}{{x}}^{{3}}+{9}{{x}}^{{2}}-{30}{x}={3}{x}{\left({{x}}^{{2}}+{3}{x}-{10}\right)}\usepackage{cmbright}\Huge\$ .

Then factor by grouping:

$\displaystyle{3}{x}{\left({{x}}^{{2}}+{3}{x}-{10}\right)}={3}{x}{\left({{x}}^{{2}}-{2}{x}+{5}{x}-{10}\right)}={3}{x}{\left({x}-{2}\right)}{\left({x}+{5}\right)}\usepackage{cmbright}\Huge\$