$\displaystyle{\left({x}+{5}\right)}{\left({x}+{7}\right)}={{x}}^{{2}}+{7}{x}+{5}{x}+{35}={{x}}^{{2}}+{12}{x}+{35}\usepackage{cmbright}\Huge\$ , not $\displaystyle{{x}}^{{2}}+{12}{x}+{27}\usepackage{cmbright}\Huge\$ . You first need to find two numbers whose product is 27 and whose sum is 12.