You incorrectly tried to combine $\displaystyle{4}{{z}}^{{2}}\usepackage{cmbright}\Huge\$ and $\displaystyle{5}{{z}}^{{3}}\usepackage{cmbright}\Huge\$ , as well as 10 and $\displaystyle-{2}{{z}}^{{2}}\usepackage{cmbright}\Huge\$ , but these are unlike terms and cannot be combined. Regroup and combine like terms to find the sum.