You multiplied the first terms and the last terms, but you forgot the middle term. Use FOIL to multiply two binomials. To get the part that is missing, multiply the outer terms, $\displaystyle{\left({2}{x}\right)}{\left(-{2}{y}\right)}\usepackage{cmbright}\Huge\$ , multiply the inner terms, $\displaystyle{\left(-{3}{y}\right)}{\left({6}{x}\right)}\usepackage{cmbright}\Huge\$ , and add these to the terms you have.