$\displaystyle{27}={1}\cdot{27}={3}\cdot{9}\usepackage{cmbright}\Huge\$ . The factors whose sum is 12 are 3 and 9. Now rewrite the trinomial and use grouping:

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