First identify the like terms. Then combine them by adding coefficients. Remember that $\displaystyle{{y}}^{{0}}={1}\usepackage{cmbright}\Huge\$ .

$\displaystyle{11}{{y}}^{{2}}-{6}{{y}}^{{2}}+{12}{y}-{8}{y}+{5}{{y}}^{{0}}={\left({11}-{6}\right)}{{y}}^{{2}}+{\left({12}-{8}\right)}{y}+{5}\cdot{1}={5}{{y}}^{{2}}+{4}{y}+{5}\usepackage{cmbright}\Huge\$