You may have thought that you could combine unlike terms by adding coefficients. You can only combine terms with the same variable and exponent. The given polynomial equals

$\displaystyle{\left({11}{{y}}^{{2}}-{6}{{y}}^{{2}}\right)}+{\left({12}{y}-{8}{y}\right)}+{5}{{y}}^{{0}}\usepackage{cmbright}\Huge\$ , and you need to combine the like terms in the parentheses.